ItalianZ32

I have a 92 Camaro 305 TBI with a 5 speed. It has been idling and running poorly as of late and I was hoping to get some feedback. I have read countless posts about this issue, but still cannot seem to get to the bottom of my issue. I know everyone on here has a lot more knowledge than I do so I was hoping someone might have seen this before and could help me before I throw any more parts at the car. I am saving up for a 350 swap, but I want to get it running again since that is not going to happen this year.

Here is the issue: The idle jumps from 400 and almost stalling to 1800 or so and back again. If I try to drive the car it bucks and studders really bad in 1st and 2nd gear and runs better in 3rd and up but feels like it lacks power. It is not throwing a code or anything.

Parts I changed and why:
IAC valve(Was told this could be my issue and easy enough to change)
EGR Valve and Solenoid(when I manually push this open(or closed??) the idle smooths out)
Injectors(I had a leaky injector so I replaced both)
Fuel pressure regulator( I had this open from changing the injectors so why not)
MAP sensor(voltage test showed 5 volts at idle and a WOT, also unplugging this made the idle smooth out)
Fuel Filter(just seemed like a good idea)

Parts I have not changed and why:
Coolant Temperature Sensor(Wanting more feedback before throwing more parts at the car)
Throttle Position Sensor(same as above)
Fuel Pump(Mechanic said I have good fuel pressure)
PCV Valve(opens and closes with ease so I didn’t think it would be stuck)

A few things to note. I did some testing and when I unplug the MAP sensor the idle smooths out. Assuming this is because the ECM is reading that it is unplugged and goes into keep the car running mode. But it also runs smoother if I keep the MAP sensor plugged in but unplug the vacuum line that runs to the MAP sensor. It also runs smoother if I manually push open the EGR valve. So my theory is that the car is not getting enough air and too much fuel. I am just not sure why and what else to check or test. I tried checking the vacuum lines for leaks but have not found anything yet. Is there a way to test the CTS or TPS? Let me know what you think. Thank you!

JA411

Scan data or do volt measurements, usually vacuum leak or running rough / missing. Test with know go MAP sensor

Ron U.S.M.C.

There is a procedure called "Setting Minimum Idle Speed".
In it you will be "re-setting" the IACV "Properly.

You will need a Digital Timing gun that shows Idle speed or a similar digital tack.

The procedure looks like this and is something most cars will need to have done.
Especially if the cap on the Idle screw has been removed.
You cant just start turning the screw attempting to adjust it like so many do.

Anyway, here's how to set it for my car.
Yours should be similar,possibly a 5 speed could be slightly different and some of the guys here could chime in if that's true.

"Setting Minimum Idle Speed"
1) Jump the A to B terminal under the dash.
2) Turn the key on but do not start it.
3) What 45 seconds,you should hear a slight ticking coming from the IACV.
4) Then unplug the IACV with the ignition still on.
5) Disconnect the EST wire and remove the jumper.
6) Start the car.
7) It may be necessary to hold the throttle open slightly to prevent the engine from stalling.
8) Allow the engine to reach normal operating temperature.
9) Connect a tachometer. I used a digital timing gun with RPM feature.
10) Adjust the minimum idle speed using the throttle stop screw.
11) My Chilton’s says set it to 700rpm in park on an 89 TBI 5.0 auto.
12) When done shut the car off and reconnect the EST wire.
13) Plug the IACV back in.

Drive the car easily at first allowing the ECM time to learn the new parameters.

This is the "base" you need to build on. If this is off so will be anything you do to the engine in search of a solution to other problems.

By the way, finally after months of searching a friend here helped me with this and it was a night and day difference.
I could barley keep it running and was stalling at every light.

This helped fix that.

This is good advice for anyone having similar problems.

SandmanSS

I can't find a thread on Fuel pressure regulators and I can't figure out how to ask a question or start a new thread. that being said, I replaced fuel injectors today and saw what looks to be the remains of an explosion/meltdown on my fuel pressure regulator. is thing trashed? new regulator and rails now?

CDG11b

I had the same problem, it was a wire near the head I believe that was loose and needed replaced. It's been awhile so I can't remember exactly what it was, hope this might help.

ItalianZ32

Thank you. I am going to try to look into resetting the minimum idle speed and I will see if ican have someone also check volt measurements and I will see where to go from there.