Astina 89 BG will not rev past 2500 when warm

[Eno]

My sons 1989 Mazda Astina BG DOHC has a problem. It starts and idles & revs fine until it warms up, once it is warm which takes 1-2 minutes if you increase the revs it gets to 2500 RPM & then dies & then back to 2500 & repeats this up & down cycle. It starts fine & revs normal every day until it warms up. I'm open to any suggestions, it's my sons & he can't just buy parts on a hunch, he needs to prove a part is faulty but I've wasted too much time on it so please please HELP!!
The dash temp gauge shows the normal expected temps.
I have tested many things but recently I've just helped him out with buying some second hand parts to eliminate things, here is what we have changed:
MAF
TPS
Choke (IAC or idle air controller, or idle speed controller ISC, the thing on the TB that's not a TPS)
ECU
Engine temp sensor
Fuel filter (in engine bay & fuel tank)
Fuel pump
Fuel regulator
Plugs
HT Leads
Complete distributor
Coil

There are no computer error codes & all the air & vacuum pipes look ok.
I can easily take voltage & resistance measurements if someone knows what to check.
Here's a link to a Youtube video of the car revving up & down by itself when warm whilst applying a little constant throttle: http://youtu.be/a8D3IpVmIPk

[NaughtyGT]

Well ,I would have suggested the TPS or CTS. It should throw up a code to let you know what sensor is playing up (if it is indeed a sensor?)

Have you changed the air cleaner? I know it seems rediculous but.......

02 sensor would be the next thing I guess if you can find a cheap 2nd hand one?

Failing that. Leads, dizzy, coil/coilpack?

[Clean_Cookie]

Not sure if I recall correctly but didn't someone have a similar issue and it was the dizzy/ o ring seal, after it got warm oil leaked into it and made it run really rough? Maybe worth opent it and seeing if it's dry inside. Asanga had an epic detailed guide in his project worklog.

[Old Grey]

Do you have the manual
1992_NoAm_Protege_Service.pdf

http://www.mazdabg.com/ftp-uploads/Mazda/323/

Probably not your problem but my RX7 S4 does that when the throttle switch isn't adjusted properly. I found it by depressing the switch while reving it.

Did the problem just appear one day and still continues continuously. Maybe think back to what happened on that day, eg, hit a bump that may have broken a wire off one of the Gbox switches.

Sounds like when it's running on cold rich cycle it's fine, but when it's hot normal cycle something is telling it to cut the fuel.
Maybe put a timing light on it and see what the spark does, if it's consistent it's probably something fuel.

[Eno]

Thanks to everyone that has responded so far, please keep thinking about this, if I sound desperate then it's because I am. I've tried to do all my replies in the one post, not sure if it's the way to go but I've done it anyway.

Thanks NaughtyGT
The air filter is clean.
I was told by a few people that if it was the o2 sensor it would only be a problem during motorway driving only, I don't know if that is correct but a second opinion on this would be good.
I have already changed the leads (just added that to main post).
I have looked inside the distributor cap, gave the contacts a clean but it all looked fine.
I haven't done anything more to the distributor & I haven't changed the coil, but it sounds fine, it doesn't sound like it's missing & only happens when the engine is hot after 2 mins so I've discounted that.
Please let me know if I'm wrong in these assumptions as they are not based on experience!

Thanks Clean Cookie
The inside of the distributor cap was completely dry & very clean, I haven't looked any further than that though.

Thanks Old Grey
I don't have a Protege Manual.
What is a throttle switch, I've replaced the TPS (Throttle Position Sensor) is that the same thing?
The vehicle doesn't get used much, it's my sons & I was using it to teach him to drive, so it just happened one morning in the driveway whilst I started it to top up the battery voltage, it's never been driven since.
Unfortunately I don't have a timing light.
I'm assuming that the air to fuel mix should be slightly different when the engine gets warm, & it is this lack of change that causes the problem. But if I start it when cold & leave it to idle I can here something change when it gets hotter, presumable the choke doing it's thing so now I'm just not sure.

[rodhog]

Eno was thinking about your problem for a while and something I came to think about.

Mazda use to put a solenoid on the line to the fuel pressure regulator.

The Idea being to remove any what old cars had in terms of vapour lock.
Not sure if the BG BP had it I know latter models did not.

Just check the line between the fuel pressure regulator and see if it has a direct route to the a vacuum source.

Similar issue came up on a few Mitsubishis recently similar age car.

And yes TPS / throttle switch same. But some cars carried a separate idle switch. Latter models had it built into the TPS.

[Eno]

Thanks Rodhog
I think I'm going to struggle to find this solenoid vapor lock thing or even the fuel pressure regulator but I'll do my best along with Google. Any help from others to pinpoint this would be good.

I also have an idea of what it might be but maybe someone can check it for me, if I unplug the choke or the MAF when the engine is running then it definitely makes a big difference, all good so far.
But if I unplug the TPS when the engine is running it seems to make no difference at all, I tried this whilst the engine was hot & the fault was there, I tested it while idling & also when applying the throttle but the fault did not change at all, in fact there was no change ever.
The assumption I've come up with is that the TPS signal may not be making it back to the ECU. I believe the TPS that my BG has only signals fully closed or fully open so maybe the ECU doesn't know there's a fault because it thinks the TPS is always closed & therefore it should be idling.
Plus Old Grey posted something about a similar problem with his TPS on his RX7 S4.
I've changed the TPS so I know it's not that so maybe I will trace the signal back to the ECU, but it would be interesting to know what should happen if the TPS is disconnected, if anyone is willing to try this then please let me know, it's dark in NZ now so I'm going to try this in the morning.

[project.r.racing]

If you disconnect the afm/maf, then engine should just die at idle.

[Eno]

Originally Posted by project.r.racing

If you disconnect the afm/maf, then engine should just die at idle.

Disconnecting the MAF stops the engine.
Disconnecting the choke makes it idle differently.
Disconnecting the TPS does nothing which could indicate that it is the problem, does anyone know what happens when they disconnect their TPS?

[project.r.racing]

Let go back a step and see something. You explain that you have disconnected the choke. But being a electronicly controlled car, as it has a tps and afm, then it shouldn't have a mechanical choke.

100% you sure there is a choke? Cos normally on a electronicly controlled car, the has a Idle Air controller (IAC).

could be a colopsed cat converter, could be anything. without know how is settles at 2500rpm. its a guessing game. does it hit 2500 and just stay steady? does it jump from 2000-3000 rpm, just averaging 2500 mostly? does it hit 2500, then just die like no power and come alive again less 500rpm?

[NaughtyGT]

Originally Posted by Eno

Disconnecting the MAF stops the engine.
Disconnecting the choke makes it idle differently.
Disconnecting the TPS does nothing which could indicate that it is the problem, does anyone know what happens when they disconnect their TPS?

that's interesting! you swapped the TPS? When you say nothing happened. That isn't concrete proof that it is the problem though. How would you know it isn't something else in the first place? If it is, the TPS will still act the same. You follow? If you were trying to see which lead of the 4 leads to check was faulty then yes, if removing one lead made no difference. Then that would be the lead.....

[Old Grey]

I've got the 91 BG with BP SOHC engine, and when I disconnect the TPS plug the idle goes up a touch, and the engine stills revs normally - no hunting -.

The way the RX7 works is, if the throttle switch isn't depressed when hot the ECU thinks the engine is still idling, and that means it won't get out of the idling fuel map when the revs increase.

Similar things happen when there is a air leak between the MAF and the engine. More revs require more fuel, but the flapper door in the MAP is closed, indicating it's idling. Try manually opening the flat when you rev it.

The Gbox also has a switch to tell the ECU when the engine is in neutral or driving - my wire broke -. It's a long shot, because it only effected my idle quality and not the hunting problem you have, but it's worth a look.

What it sounds like is something is telling the ECU that the engine is still in idle mode.

You can short the connector in the plug to keep the fuel pump running and see if that makes a difference, and even clamp the return line for even more fuel pressure. This might indicate the fuel map isn't switching to drive mode.

[Eno]

Originally Posted by project.r.racing

Let go back a step and see something. You explain that you have disconnected the choke. But being a electronicly controlled car, as it has a tps and afm, then it shouldn't have a mechanical choke.

100% you sure there is a choke? Cos normally on a electronicly controlled car, the has a Idle Air controller (IAC).

could be a colopsed cat converter, could be anything. without know how is settles at 2500rpm. its a guessing game. does it hit 2500 and just stay steady? does it jump from 2000-3000 rpm, just averaging 2500 mostly? does it hit 2500, then just die like no power and come alive again less 500rpm?

I actually called the thing an air bypass solenoid at the Mazda used parts dealers & he said the thing in my hand was a choke so I called it a choke on this forum, oops should have stuck with IAC but I'm still learning.
Have a look at the video, I posted a Youtube link in the original post, this will give you some idea of how it revs up & down.
In the video I tried to show it idling ok at the beginning & then I added some throttle & showed it revving up & down by itself, then I added more throttle & it just revved up & down by itself with a deeper tone & then I let it go back to idle. I hope this helps.

[Eno]

Originally Posted by NaughtyGT

that's interesting! you swapped the TPS? When you say nothing happened. That isn't concrete proof that it is the problem though. How would you know it isn't something else in the first place? If it is, the TPS will still act the same. You follow? If you were trying to see which lead of the 4 leads to check was faulty then yes, if removing one lead made no difference. Then that would be the lead.....

I installed a second hand TPS & there was no change, fair enough, it's probably not that then.
But I disconnected the TPS cable when the engine was at idle & the revs & everything were the same. I then disconnected the TPS whilst adding some throttle & there was still no change. This sort of indicated to me that although the TPS itself was ok there maybe a problem with getting the signal back to the ECU. Just a guess but it seemed logical.

[Eno]

Originally Posted by Old Grey

I've got the 91 BG with BP SOHC engine, and when I disconnect the TPS plug the idle goes up a touch, and the engine stills revs normally - no hunting -.

The way the RX7 works is, if the throttle switch isn't depressed when hot the ECU thinks the engine is still idling, and that means it won't get out of the idling fuel map when the revs increase.

Similar things happen when there is a air leak between the MAF and the engine. More revs require more fuel, but the flapper door in the MAP is closed, indicating it's idling. Try manually opening the flat when you rev it.

The Gbox also has a switch to tell the ECU when the engine is in neutral or driving - my wire broke -. It's a long shot, because it only effected my idle quality and not the hunting problem you have, but it's worth a look.

What it sounds like is something is telling the ECU that the engine is still in idle mode.

You can short the connector in the plug to keep the fuel pump running and see if that makes a difference, and even clamp the return line for even more fuel pressure. This might indicate the fuel map isn't switching to drive mode.

Thanks, I like the idea that the idle changes slightly when you disconnect your TPS, & nothing changes when I disconnect mine, that still gives me hope that maybe my TPS signal is missing.
I agree with the idea that the ECU thinks it is always in idle, & if it thinks the TB butterfly is closed because of a hypothetical TPS signal fault then this could be why it thinks that, & another indicator towards the theory of the TPS signal.
I had already tried opening the MAF flap more to see what happened but it just made it worse, plus I've changed the MAF so it shouldn't be that plus the engine dies if I disconnect it so it must be doing something.
I'm a bit reluctant to mess with the fuel pump & return line but if the TPS signal tests ok then I'm willing to try anything.
The car is a manual, will it still have one of those neutral wires you mentioned?

[Old Grey]

Originally Posted by Eno

Thanks, I like the idea that the idle changes slightly when you disconnect your TPS, & nothing changes when I disconnect mine, that still gives me hope that maybe my TPS signal is missing.

I'm a bit reluctant to mess with the fuel pump & return line but if the TPS signal tests ok then I'm willing to try anything.

The car is a manual, will it still have one of those neutral wires you mentioned?

The idle goes up maybe 50rpm when disconnected.

The fuel line thing is easy. Find the return line in the engine bay. Put a piece of a rag or rubber around it so it doesn't get damaged. Gently grab it with pliers until the flow stops. Page F-29 of the manual.

The gbox also has a clutch switch at the pedals.

[Eno]

Originally Posted by Old Grey

The idle goes up maybe 50rpm when disconnected.

The fuel line thing is easy. Find the return line in the engine bay. Put a piece of a rag or rubber around it so it doesn't get damaged. Gently grab it with pliers until the flow stops. Page F-29 of the manual.

The gbox also has a clutch switch at the pedals.

Ok, so I clamped the return fuel line but nothing changed, I like the concept but unfortunately it didn't work.

I also tested all the ECU pins whilst pushing the clutch in & out but I didn't find any 0v signal that went on & off. This may indicate a problem with the clutch switch or maybe the clutch switch is only for cruise control which I don't have, does anyone know? Should I be able to see the clutch switch on or around the clutch pedal from the foot well (whilst upside down with my head in the foot well of course). I've put that bit of pain off for now & time for lunch.

I also traced both open & closed TPS signals back to the ECU as well as checking the middle pin of the 3 was 0v, all ok there. I was pinning my hopes on that, but I love the car & I haven't given up yet. (close though but at least I'm learning stuff)

Ok so what next, remembering that the fault only happens when the engine is warmed up after approx 2 mins. Until then I can rev the nuts off it.

[Old Grey]

Did you jumper the service connector to keep the fuel pump on page F-122 - a long shot as insufficient fuel pressure doesn't hunt regularly -

Clutch switch is page F-172 - this is a long shot also -

Did you try the TPS test on F-169

Try reving it with the fuel cap off - maybe faulty purge valve reducing fuel pressure -

Unplug the ECU and plug it back in a few times, maybe connector is corroded and not connecting. The electrics go weird in my RX7 when left sitting for long periods, driving usually shakes them into working.

[Eno]

Originally Posted by Old Grey

Did you jumper the service connector to keep the fuel pump on page F-122 - a long shot as insufficient fuel pressure doesn't hunt regularly -

Clutch switch is page F-172 - this is a long shot also -

Did you try the TPS test on F-169

Try reving it with the fuel cap off - maybe faulty purge valve reducing fuel pressure -

Unplug the ECU and plug it back in a few times, maybe connector is corroded and not connecting. The electrics go weird in my RX7 when left sitting for long periods, driving usually shakes them into working.

I've managed to find a manual for a 1992 US Protege that looks similar & the page numbers seem to match up with your post.
The TPS has been thoroughly electrically tested & also replaced, plus the signals have been traced back to the ECU so I have discounted that.

I removed the fuel cap but it didn't make any difference, good idea though.

I found the clutch switch but it was not being used, there is a hole on the clutch pedal arm that allows the micro switch activator to pass through meaning that the switch doesn't get used. This seems a bit odd but to make sure I managed to activate it but the fault remained.
I haven't checked the gearbox neutral yet, but I did check all the ECU signals whilst putting the car in & out of gear & there was no signal, so a bit more work to do there, although with my very limited experience I can not see why it would make any difference whether it is in gear or the clutch is being used or not but none of my ideas have worked so far so I have to try new stuff.
I still have the fuel pump to jumper on to increase pressure, I'll get around to that tomorrow, the rest of today I now have a dishwasher to fix, does it never end.

I would like to thank everyone that has helped so far, any other ideas of things to try are more than welcome.
Remember that the fault is fine until the engine heats up, there are also no fault codes & I have replaced a whole bunch of stuff.

[Old Grey]

The gbox and clutch switch are long shots - my 323 ran fine with the broken wire but idled rough -.

Even though I'm hinting at a failing fuel pump - maybe it's limited to a low pressure - when they fail they don't act regularly like in your video - mine idled but would break down with any load -, so that's a bit of a long shot also. But at least jumping the pump will rule out the fuel relay.

My RX7 idle switch did the exact same thing your does, revs cold hunts hot, but the odd thing is the rpm yours does it at. My RX7 did it at 1200rpm, but yours does it at 2500rpm, and it's the 2500 that rings a bell. I was chasing a high fuel consumption problem, and I remember there was something in the manual where you have to check something above and below 2500rpm. I can't remember what it was exactly but I remember something like that.

You could try
http://fordlaser.com/forum/index.php...24fc7f5e8f2e51
I think they have more mechanics there. Just tell them it's a BP DOHC engine