Hey guys I recently took my 1996 z28 to a local shop to have the tune up done plugs, wires, optispark and all. Now my car when stopped at a light or even in park will start to give itself gas on and off. It revs on its own. Never too strong, but strong enough to try to go even when you have your foot on the break. The mechanics at the shop can't figure out why its doing that and i wanted to see if anyone knows what this might be. Please help.

 

Did you name your car Christine?

Without being there to see just exactly how powerful the revvs are I am only able to venture a guess that the IAC could be cycling and unable to get a good idle. This can be caused by the O2 sensors, Timing not set right, bad IAC, AIT sensor not working right and if you have a MAF (cant remember if the LT1 has one or not) it may not be reading right. If you do have a MAF make sure it has a screen. It is there for air control not for keeping stuff out. If it is gone the airflow around the sensors are going to be uneven and that causes all sorts of issues. Also the Air filter is what keeps the debris out of the MAF.

Hope this helps. If you have a CEL on right now have the codes read and let us know what it says.

Massey

 

Yeah, Christine is her name!

Im uploading a video of what it sounds like.

They did change out the water pump which they said they needed a timing seal for. So I'm not sure if they messed up the timing at the same time? If this were the problem, is it as simple as adjusting the timing, or is it more complex?

im not sure what a MAF is, so I dont know if it has it.

ill post the video soon.

 

Watch "20140217_202533.mp4" on YouTube
Here is the video in the driver seat.

And yes the service engine light is on. Its throwing a code that I dont rember. It has to do something with Evaporative Emission Control Systems.

 

 

No, they didn't mess up the timing. They replaced the water pump drive shaft seal that's on the timing cover. That's done externally, and has nothing to do with the ignition timing, which can't be adjusted mechanically anyway.
An evap issue is often a vacuum leak, which would make the engine run erratically. Get that taken care of, and oh, put some gas in the tank. Running it on fumes is bad for the in-tank fuel pump. It's an electric motor, and being submerged in gas has a cooling effect. Might be a long shot, but with being that low on gas the pump might not be sucking a consistent flow of fuel.

 

First off write the code and post it so we have a direction... then maybe...

Check for vacuum leaks and possibly a stuck open purge valve for the evap system... your o2's and map sensor should give you an idea on whether it is sticking or not as well. A purge control valve is like have a vacuum leak and can happen intermittently. O2's will read lean and short term fuel trim will be positive during the event if its a vacuum leak or a purge valve issue.

 

Thank you everyone for the speedy replies. I switched out the IAC. Still the same. The mechanic did say the vacuum hoses are all cracked, there are about three hoses like this. So this may be the cause of my problem. I tried to buy these hoses at the auto store but they dont carry these. Not even the dealer sells them. Anyone know where I can find these?

 

If you're talking about the hard plastic lines being cracked, then yes you have vacuum leaks. Work back to where the line isn't cracked, cut it carefully there, and splice them with rubber vacuum hose.

 

Most of the hard plastic is fine. The rubber vacuum hoses that they connect to are cracked wide open. Like for instance the elbow L shaped one. How do I replace this? And does that sound like what could be causing the problem? Thanks!