2.8 V6 MPFI


For the past week or two I've been having a problem with the idle. It's been sticking around 1500, sometimes almost 2000, sometimes 1200. Before the problem started it would idle almost perfectly at 800.

The initial problem started after I cleaned out the throttle body and plenum with some Throttle Body Cleaner for fuel injected cars. It is supposed to lubricate, too.

These are the things I've done to try to fix the problem:

1. WD40ed the throttle cable/spring

2. Replaced IAC

3.Adjusted TPS, but not with a digital Volt-ohm-meter, just twisting it until it idled as low as it would. Ended up being in it's stock position so I don't think anything is wrong with it.

4.Checked vacuum hoses. Sprayed the throttle body cleaner over the lines and connections looking for RPM changes.

5.New upper throttle body plate gaskets, to make sure IAC and all weren't leaking.

6.Used some silicon gasket sealer and even dabbed some around some suspected leaky vacuum connections.

7.Messed with minimum idle screw. I regret that.
To the present...

Now sometimes it idles fine and sometimes it idles high.
It's wierd because sometimes the TB plate does stick and when I push it back it idles back down, but other times it idles even higher but the TB plate is closed.

At one time today it was really hard to get the car to turn over. The RPMs slowly rose from 0 to 1000 but took about a full 5 seconds to do so. Weird.

Today I ran into a new problem. I was driving, doing about 45 and put the car in nuetral to roll up to a turn. As soon as I did the RPMs slowly started dropping. 800...700...600...500...and the engine just died.

I got a Check Engine light at this point. The first time I'd gotten a light the whole time this ordeal has been going on.

I started it back up and a minute later it did it again. Then sometimes it would idle at 500 and go back up. 500 is very low for what my car used to do.

Once home I adjusted my minimum idle screw since I'd previously brought it down. I was about to go out again and thought just as a precaution of I set it higher then I'd be reassured that the car wasn't going to stall out, atleast until I could check it further. I never stopped the engine during this.

I got back in after dropping my sister off at the house and it was idleing at the same number. I thought that was weird because I expected it to be higher since I'd adjusted the minimum idle screw. Maybe my IAC adjusted for it.

I went up to Advance Auto Parts so they could quickly check my code. But after turning my car off, once they came out to check it, there was none. Guess I'm gonna drive around with a bent paper clip now so when I get a code I can quickly pull off and check it because I'm really curious what my ECM just all-of-a-sudden found.

Summary:
-High idleing.
-Normal idleing.
-Stalling car.
-Hard to start once.
-Random SES light that only stayed on for about 10 minutes.

My next guesses are the EGR. Anyone that would like to share how to go about testing this? I need it clarifyed because I read on one thread that you can push up on the diaphram and it shouldn't stall...or should? I pressed up on mine after just starting it and it started to stall but never fully did. Maybe if I held it longer it would have. I pulled the vacuum hose to it and covered it with my finger and nothing changed at all. I thought it would work both ways. Maybe this suggests a vacuum leak? I haven't found one...

Thanks for taking the time to read.
Opinions?

 

Remember, anytime you mess with the idle screw, you have to adjust your TPS. You should go to Radio Shack and get a cheap voltmeter. I think that on the 2.8 it's supposed to be at .6 volts when the ignition is on, but don't quote me. If you don't have the TPS keyed in, you're going to have all sorts of weird problems, including the car dying on you while you're driving it.

 

Really? Even though the idle screw is not electrically connected to anything? I guess it's just becausethe throttle plates are at a different position when it's idleing? Guess I'll do that. Buying a new one probably wouldn't solve anything huh? I'd still have to set it correctly?

 

I had the EXACT SAME PROBLEM on a 1987 Fiero 2.8 after we did the cylinder heads.

It was a plague of vacuum leaks...

There is a really big line under the plenum that was unhooked on ours. Sometimes the line would just "block" the hole that it was supposed to be hooked to and run fine and then it would fall off and go nuts again...

Everything you're saying is what happenned to us. Do yourself a favor and check ALL of the lines again... and again... and again...

Did you remove the upper half of the plenum? That is where all of the big lines hook up...

 

I never removed the upper plenum, but that'll be something to look into if I can't do it any other way. It's my everyday car so my days doing longer work on it are limited. Thanks for the input!

 

also don't forget to check your vacuum brake booster by plugging the line that goes to the booster...