Anyone have anything else to add? Are there any good diagnostic tools that I don't already have that I can pick up to help me out?

 

My 88 s10 does this but only on a cold start.....

Does it get better if you get the RPMS past 3000 then let it go back to idle??

How are you reading TPS voltage and so on? Multimeter or ALDL?

If you don't have it already you may want to invest in an OBD1 aldl cable to connect to your laptop/computer to see what the ECM is doing....

A lot of times the problem can be pinpointed just seeing the data that the ECM is putting out..


I know you said you did propane, but take brake parts cleaner or starting fluid, squirt it along all vacuum lines and listen for a rise in the engine, propane doesn't always do it in my experiences.

You may also have something simple like a bad distributer cap/rotor/module, or a loose wire somewhere.

Also check the MAP sensor, my truck runs like ASS with it unplugged, or faulty....


But the ALDL stuff with winaldl would probably be a quick/easy way for you to determine it for this time, and future times you may have issues.,

 

Idle is best when cold, but that may be because it is trying to idle higher to warm up. It is by no means good. Reading voltage with a multimeter


Do they have a good one for the speed density cars? I've seen them for MAF but they always seem to say that they don't work on MAP cars. Please point me in the right direction for an ALDL cable/program for MAP cars (or even a diagram to build the cable) if I am wrong here because I would love to do this.


I did carb cleaner too, no change. I think if there is a leak it may be in the lifter valley.


I doubt its just a loose wire. I have tested every sensor several times along with unplugging and plugging in all wires to them. I may have a sligtly bad distributor, but even with the EST unplugged and the timing stable at 8* BTDC the idle is still crap. I don't see how a distributor could affect the engine in any way besides the timing. Also, I tested the MAP by checking the change in output voltage vs change in vacuum. The base reading was in the normal range and it changed steadily when I changed the vacuum.


Show me where and I'll do it.

 

How would I check the coil? I don't think thats the problem since the coil and wires are both fairly new. Also, how would I find evidence of a bad IAC? Right now the IAC is the only thing keeping the idle even remotely stable so I don't want to replace it if its still good. Also, I'm tired of replacing items because they "might" be the problem. This theory is getting expensive.

 

pretty sure its not your IAC or coil..


you say the EGR is blocked off but is it by a plate or just unpluged the vac line to it?

also can you drive the car? how does it run other than the idle?



either way love the 91,92 z28.. still have a 91 myself.

 

ok stupid question but did you notice the unplugged hose over the driver side valve cover in the pic? i accidentally forgot to cap a hole on the throttle body when i removed a hose in favor of a breather and was about crapping my pants when i was getting an erratic idle and oil pressure. are you sure that the vacuum lines are hooked up in the right place?

 

The EGR is blocked off by a plate of aluminum and RTV sealant. The vacuum port for it is blocked off at the plenum. I had thought that it may have been the cause of my rough idle and when I went to get a new one all the parts stores needed to special order it. I didn't have time so I blocked it off.

There is no unplugged hose over the driver's side valve cover. There are only three hoses on that side. PCV, Brake booster, and AIR system hoses. All three are properly connected. Am I missing something?

The car runs pretty decent above idle as far as I can tell, but then again I am judgeing that against back when I had two bad fuel injectors, a bad fuel pump, and bad plugs and wires. There is still some hesitation sometimes, but I've encountered worse. It seems to rev up fine too, but then again I've never experienced it running "right".

 

I'm pretty much at a loss... sounds like you've tried everything.


maybe try unpluging your o2 and see if it runs better.

have you set the base idle? where you ground A and B (same as checking the codes) wait a min or so with the key on but not running. then unplug the IAC and the set timing plug thing, then start the car and set the idle for 450 rpm's (500rpm"s for an auto trans).... not sure if it will help much be its something free that can't hurt either way to try.

 

I have tried using that exact method, but you can't set the idle on a machine where the idle constantly changes (from 500-900 RPM). I can try unplugging the O2 but I suspect that will only put me into open loop and I'll run the same as when the car is cold. Only difference being that I might find some things that only happen in open loop when the engine is warm that may tip me off.