Hey guys, the following question is about a 94 z28 I purchased just the other day. I know its not third gen related, but there are some very mechanically inclined people on this board, and I trust that someone will be able to point me in the right direction.

The z28 has the fuel injected 5.7... I hadn't a single problem with the car in all the times i've driven it since the other day. The second I turn the keys over to my father for a spin, it started acting funny. While at a light, it starting revving up on its own to just about 1100rpms, would die down to idle, then rev again... possibly related: There is a noticeable downtime between the instant you hit the gas (full throttle) and when it actually takes off.

I'm wondering if someone could give me their opinion on what the situation could be... my father suggests it may be a dirty fuel injector or such as that.

Thanks ahead of time for any help!

 

vacuum leak possibly?

 

I have a list of things for you to check:

1. Possibly a clogged P.C.V. valve.

2. Vacuum leaks.

3. A bad E.G.R. valve.

4. Dirty M.A.F. sensor.

5. Clogged fuel filter.

6. Believe it or not, a dirty air filter.

7. The intake manifold gasket which is notorious for leaking on the LT1's.

Hope that's good enough to get you started. If none of these turn out to be the culprit, drop us another line.

 

Hey guys, thanks for the replies! I'm going to go through that list, iroczracer07, I appreciate it. I have another addition to the situation. It seems that whenever i'm idling, the temperature raises dramatically, but when you reach a cruising speed, it drops dramatically once again. We are almost sure that the temperature problem is connected to the "self revving" problem, given it only revs when hot. So, we're going to replace the water pump, thermostat, and any lines to see if that solves the problem....once thats completed, i'll let you guys know how it turns out! Thanks!

 

Just a thought about your temperature problem. If you have a means of pressure testing the cooling system and the radiator cap I'd do it. I'm dealing with a temp problem on my mom's 94 Z as we speak. The cooling system doesn't seem to be holding pressure and therefore the temp rises really high at idle, but when she drives it down the road the temp drops back down to normal. It's a work in progress. Did I mention it was frustrating too, lol.

 

So it was searching? Was the engine to temp or cold?

 

Not sure who you were posting for Red Devil, but I put the link in my favorites so I can check it out later. Thanks by the way.

 

Ok guys...quick update. The thermostat and water pump have been changed. We're still going through the process of adding coolant and making sure its full. At first it seemed as if the problem was almost completely eliminated. The tempurature would still rise at an idle, but not NEARLY as dramatically and if I sat there long enough to where the fans would kick in, it would cool off again nicely. But it couldn't have been more than a few hours to where all the problems came back in full force...the engine would start revving itself up to the 11 or 1200's even when the temperature was fairly cool, but then it would rise very quickly. So, i'm letting it cool right now and im going to see if perhaps it still needs more coolant (I don't think thats the problem though). This is a problem for me since i live around many, many stoplights. Iroczracer07, i'll keep in touch with you since we seem to have a familiar problem in terms of temp.

 

Okay, this was the solution to my problem. The cooling system was not holding pressure. After some troubleshooting, I narrowed the problem down to a bad radiator. I changed the radiator and the cooling issue seemed to be fixed until I went through the McDonald's drive thru. It didn't overheat, but the temps went real high. Tracked that down next and found that one of the fans wasn't coming on. I'll let you know what the results are after I fix the fan. Quick question though. Have you tried using a q-tip and rubbing alchohol to lightly brush the wires on your M.A.F. sensor? That might fix your problem with the idle. If it doesn't, check for a leak around the intake manifold. I've heard these were very problematic on the 94-97 LT1 Z28. Keep me posted.

 

Hey man. I bought one of those Haynes repair manuals for my car and it mentions the M.A.F. sensor but it doesn't tell me what M.A.F. stand for or what it does. Could you fill me in?? I see where it is and it looks like an easy replacement if it had to be, i'd just like to know what im fixing. Also, today I purchased a new coolant temperature sending unit, and we're going to replace that soon. After this repair, i'll check back in to tell you how things are working out.

 

M.A.F. stands for mass airflow sensor. It does just what the name implies. The little wires in there sometimes get dirty and need to be cleaned. The q-tip and alcohol will do the job nicely, but be prepared for a lot of dirty q-tips. Anyway, the M.A.F. feeds its info to the P.C.M. which determines idle quality and a bunch of other stuff. As a matter of fact, the car won't even start without it. Pull the plug when it's running and the whole damn thing stops. I finally got a temp reading from my antifreeze too. Believe it or not, the gauge in mine was wrong. When the temp was 228 actual degrees, the gauge said it was almost at redline!! Keep me posted.

 

The car will start without the MAF, it is common as one test to unplug the MAF to help determine if it, or the relays are faulty.

Again, does the engine search or is the changing RPMs stable for a time then change? Does it shut off if you don't feather the clutch? Have you checked fuel pressure yet? Does this happen when the engine is at temp only or will it do it cold as well?

Oh, add distilled water and antifreeze at a rate of 60/40. Don't just top off with antifreeze, it sucka as compared to water at thermal transfer. Water wetter works well and probably should be added if you continue to have a problem..

 

iroczracer07 and Red Devil, thank you both for your input. I will DEFINITELY test the M.A.F. now that I know exactly what it does. I know where its located as well...should be easy to test it out and/or clean it, no?

Red Devil, to answer your questions. It does seem to search, it doesn't stay stable at a higher RPM. It will raise to about 1100 then drop...1200 then drop... or if its in park, it will reach a bit higher. It will NOT shut off if you don't feather the clutch, it will always stay on. I have not checked fuel pressure yet - and it seems to start when the engine temp reaches around the halfway mark, then after that, it will do it even at the quarter mark...but it would never start doing it at the quarter mark, if you can understand that.

Any other info will be greatly appreciated, thanks!