Lose revs when accelerating

[mansonitefirefox]

'97 BAIII 1.8 Astina

Looking for suggestions for a problem my car has developed.

When the engine is cold if I accelerate beyond a feather touch on the throttle the engine will not increase in revs and sometimes even lose a few.

Also when I am braking with the car in neutral at about 900 rpm suddently it will drop down to as low as 500rpm and if I have the lights/aircon on I will visibly notice the headlights dim, the car will then kick up to 1000rpm and the lights will go back to normal.

I have my own ideas, but I want to hear what people think.

[project.r.racing]

Problem 1 - old engine syndrome. normal for old worn BP engines to do this. allow the engine to warm up a little more than you normally do. And maybe use a slightly thinner oil to allow better initial flow at start up temps.

Problem 2 - One of the most common problems to a BP engine. Faulty IAC valve. When the brake booster steals some vacuum from the manifold to assist the braking. The IAC should open up a little more to compensate for this. Dirty/blocked/faulty IAC will not allow enough air through it and the rpm will drop. Alternator doesn't run properly under 700rpm, and the extra draw from the lights strains the whole electrical system.

[mansonitefirefox]

Originally Posted by project.r.racing

Problem 1 - old engine syndrome. normal for old worn BP engines to do this. allow the engine to warm up a little more than you normally do. And maybe use a slightly thinner oil to allow better initial flow at start up temps.

Sounds fair enough... however the problem just appeared out of no where. 1 day it was fine, the next it was a big problem. I would have thought something like that would happen over time?

[mansonitefirefox]

Originally Posted by project.r.racing

Problem 2 - One of the most common problems to a BP engine. Faulty IAC valve.

Is this something a somewhat-capable backyard mechanic such as myself could fix? Or am I off to the mechanics?

[NaughtyGT]

Sorry folk have taken so long to answer dude (incl me). Sounds like a leak to me of some sort. Manifold vacuum?

Maybe the ECU is getting an iffy reading from mixture input? Like it's out of tune if you know what I mean? It's compensating by bringing the revs back up, when they've dropped as in your 2nd scenario. I would definately look @ the IAC, as projects suggested.

Perhaps their is a vacuum leak? Might pay you to trouble shoot. Annoying but, it doesn't sound like the dizzy or coil/plugs/leads as the most obvious signs then would be backfiring, weak spark syndrome of some sort......