1992 z28, 305 TPI, auto trans. 92k miles.

I bought the car about a year ago. It's in nice shape, but had been sitting for a year or so. It ran ok, but never ran great. It always felt a little sluggish. After a month or so it started running worse. Poor throttle response, very bad gas mileage (6-8 city) and it was hard to start when it was warm. It also had a high idle.

I figured that it was related to the car sitting and when i checked the codes, the o2 sensor was showing to be at fault. I replaced the o2 sensor, and the IAC valve. After I did that, I tried to reset the idle, but I could not get it to idle low at all, it would just die. I checked the fuel pressure at the rail and it was fine. Only thing was after I checked it, the valve broke and when I turned the car back on, it shot gas everywhere." It was a little better, but still felt sluggish and the hard warm start had not been fixed.

Next, it started throwing the egr code. So I replaced the egr valve and while I was in there I did the file pressure regulator and replace the vacuums lines. Again, I had a similar result. A slight improvement but not quite right.

Next, I ohm tested the injectors and 3 were found to be bad. I got a set from southbay, cleaned the intake and runners (it was quite dirty with oil) and replaced the gaskets on the intake and runners. I also did the plugs. Again, it ran better, but not great. Still sluggish, poor hot start.

Next I did the fuel filter. No change.

It still ran, and it was better than when I bought it, but not a night and day improvement.

About a week later, I was driving home on the freeway and it overheated. Temp shot up on the freeway and I pulled over. Sure enough, coolant was boiling in the overflow. I had it towed home. I checked the oil and water and found no intermix. When I tried to start it, it fired right up. I was told to check the cat pipe and found that it had come apart and was twisted and blocking the exhaust. I replaced the cat and it was way better. Still not great, but much better.

However, the next day the water pump started leaking and it was running hot again. It sat for 2 weeks while I waited for a good day to replace the pump. I replaced the water pump today.

Now it's got a new problem. After I got the pump on, it fired right up, but once it got to operating temp, it start stalling out and died. It restarted fine, but would cough and die. If you give it some gas, you can keep it running, but even than, it's trying to die. I reset the iac valve and this time it did let me set low idle, but kept dieing. This is where I am right now. It's not showing any codes. It's low on gas, but the gauge is still showing about 1/8 of a tank.

If anyone has an idea of what to do next, it would be much appreciated.

Edit: I also replaced the coolant temp sensor for the gauge and the fuel injection system.

Reed

 

What happens if you disconnect the IAC altogether and set the idle speed via the throttle blades only? It'd be a test to bypass the IAC and see if that's the root of your problem. If the car idles fine by getting air only through the throttle blades, then you know the problem is somewhere in the IAC system. Could be something as simple as cleaning out the IAC passages in the throttle body, as opposed to the IAC motor itself.

Does the car drive ok once you're off idle?

Do you have a scanner?

 

It runs about the same with the iac connected or not. Still runs for a minute or three and than dies.

I reset the iac thinking that might be the issue, but it did not fix it. However, every time I tried to set the minimum air idle before, it would just die and I could not get it to keep running. It would only idle at like 1.6k. Now, when it runs, it will idle at 900-1000. It will run for a minute or three and than cough and die.

I don't have a scanner, I've just been doing the paper clip trick to see if it has any codes

 

It's hard to diagnose these things without a scanner. Especially remotely over a message board. You end up guessing and throwing parts at it.

How's the ignition system? Maybe the coil is giving out and you're not getting sufficient spark energy?

 

New development: I added 5 gallons of gas to the car and when I did a major rush of vacuum came out. The car ran the same. I took the gas cap off and an even larger vacuum rush came out. I tried starting the car with the cap off and it would not start. I put the cap back on and it started but still ran like garbage. A few times it will start and run good, but when I give it gas, it revs and dies when it's trying to come back to idle.

I also noticed that when its stalling, it's not sending out black smoke. It missing pretty bad, and I would think that if it was getting fuel, it would be sending out black smoke and would smell like gas. There's no smoke and no gas smell.

Do I have bad timing and and the fuel pump died right after I replace the water pump? I'm going to get a pressure tester tomorrow and see if it's got decent pressure.




QUOTE=ULTM8Z;5989686]It's hard to diagnose these things without a scanner. Especially remotely over a message board. You end up guessing and throwing parts at it.

How's the ignition system? Maybe the coil is giving out and you're not getting sufficient spark energy?[/QUOTE]

 

yeah, and check your idle vacuum too if you can get your hands on a vacuum gauge. A factory 305 TPI I'd expect to have somewhere around 19-20 inHg at idle in neutral.

 

First off, thanks for the help so far. It's been a big help.

I rented a fuel pressure tester this morning and I think I need a pump. At prime, I have 9 psi. When the car will run, it creeps up to 28-30. I tested it a few times and got the same results.

I have replaced the fuel pressure regulator, so it sounds like the pump failed right after I replaced the water pump.

Before I replace the pump, anyone have another thing I should check?

Thanks again!

 

If it indeed can't get any higher than 28-30 psi, and you're sure your fuel filter and regulator are good, then yeah, probably the pump is on the way out.