Have an idle problem/vacuum leak:

Change the ivac and also the tpi today. No different. Dave says its most likely a vacuum leak as I have all the original lines still going to the trottle-body. So....the ECM is trying to compensate. I agree.

Has anyone had this problem and been able to identify which vacuum lead from the trottle body it was? I though by posting we may find a common denominator? 

Below is some extra info:

(problem original started with economy ECM chip which was set for a lower fuel pressure - around 32lbs on start-up. Changed to performance ECM chip for the summer which seems to require about 40 lbs on start-up.) problem with 40lbs fuel pressure on start up seems to cause flooding on start-up and a constant service needed amber light on dash. So....I've turned the fuel pressure down to 32lbs again and she fires, but needs a few good blips on the trottle to get an idle of 1100 rpm. Once I get going and the engine warms I get the same problem with high idle and the service light on. Actually if I'm at a red light - I turn off the engine and restart, this gives me a perfect idle of 1000 rpm with a warm engine, untill I pull away and we start all over again with the variable idle, with fuel pressure at 32lbs - idle fluctuates between 2000  rpm and 1500 rpm, when Fuel was set at 40lbs - idle was as high as 2300 rpm and 1500 rpm - occasionally with both settings the idle may dramatically and suddenly drop down to 800 rpm.)

Appreciate thoughts.

Cheers - FieroZen Red 86 GT (19 lb fuel injectors)

Hmmm.... Nigel, it's odd that your idle speed is able to be "normal" for awhile before it screws up again. I would think if it was the usual kind of vacuum leak (like a cracked vacuum line or EGR tube) that the idle speed would always be too high.

It sounds more to me like the IAC (Idle Air Control) valve is not working properly. I know you've changed the valve, but there's always a chance that possibly the wiring to the IAC has an intermittent short.

You must be getting codes. What are they?

One thing you might try is to pull the wiring plug off the IAC while it's idling normally and see if the idle speed remains constant. If it does, you've narrowed down the problem. If it doesn't, well you've still narrowed it down as you could then eliminate the IAC as the culprit for the erratic idle.

      We had the scan tool hooked up, his IAC is dropping to 0, and if checked the vacuum port for the IAC, there is zero air coming in, so the idle has to be one hell of a vacuum leak and the IAC just can't cope with it.

             I told Nigel we need to pull his plenum do the standard re-arrange of the hoses and lines like we did with Brian's car.  It is a really good mod, if you know what each of the ports goes to and how to re-map the lines removing a lot of the extra bits that are not really needed. 

Capt Fiero wrote: ...so the idle has to be one hell of a vacuum leak and the IAC just can't cope with it.

Dave, I'm certainly not suggesting it can't be a vacuum leak (as we're all shooting in the dark at this point), but do you have any idea what might be allowing it to be so inconsistant? In other words, what kind of leak could be opening and closing again to this degree?

I take it the EGR is totally blocked off?

Nope his EGR is functional.  Well mechanically functional, however I do believe the ECM has been disabled in the ECM. 

               When you shut down the engine even for a few seconds the IAC pulls back out to give the rpm a quick jump when you start the car.  As different metals expand and contract, it can increase and decrease a vacuum leak.   There are a ton of things that can cause an idle problem, but regardless of what it is, with the IAC closed completely, that is the only thing that will cause an engine to rev.

Too much fuel will actually lower the idle, only other thing is too much air, we just have to find out what it is.

Capt Fiero wrote: Nope his EGR is functional.  Well mechanically functional, however I do believe the ECM (edit - you mean EGR) has been disabled in the ECM.

The EGR could be a potential source for vacuum leaks as well then (of both exhaust gases and/or outside air) if it hasn't actually been blocked off. Not only could the EGR tube be cracked (letting in air), but the EGR valve itself could possibly not be seating properly (letting in exhaust). The diaphram in the EGR could even be leaking (letting in air).

If Nigel doesn't use his EGR, it might be a good idea to block the EGR tube at the intake plenum end, and/or just take the whole EGR valve right off. This would at least eliminate another variable.

check the vacuum line running into the egr solenoid just as they bend arround the thermostat housing area

theres a couple of 90 degree bends in the lines

mine were kinked and one actually cracked, but not all the way thru

created a variable idle depending on the crack openning

We fixed it today, after a few hours of tearing things apart.   There were actually a combination of a few things.   The primary high idle was due to a cracked EGR pipe, a faulty TPS and a slow acting IAC.  Also a very gummed up IAC port, a broken plug wire, and a few other minor things.

          In the end we did a major delete on 90% of the vacuum lines, removing 9 out of 10 of them.   There is no more EGR system, no more Vapor canister, and a bunch of other things removed.

  From what I understand the car is running good now, just need to get a new prom chip that is optimized for the engine.

Update:

Firstly; Thx Dave. What a trooper - long day. For me, I  loved the learning experience. This is what being in a car club is all about. Hands-on figuring out the issues via experience.

Granted its a cool evening, the car ran as smooth as silk and idled around 1000 rpm at traffic lights after a highway run mostly at 100 km speed for 15 mins + Finally the ECM was able to get eveything sorted. Also a lot quieter and good pick-up in fouth gear at 100km to 160 km - OK....just to try it -