Hey guys! About 3 weeks ago I bought this 1995 Z28 and when I was testing it before purchase the engine seemed to be in really decent shape. About 2 weeks ago when I started the car in the morning the idling RPM were jumping from 500 to 1400 and the car was eventually dying. I replaced the IAC, cleaned vacuum wiring a bit, after it didn't help I took the car to my mechanic and he replaced gas filter and the black plastic thing that is next to IAC valve further along the manifold and adjusted idle for some reason, but that didn't help either. Next morning I decided to drive the car as it was and surprisingly after about 10 mile drive it went back to normal by itself. This problem hasn't yet came up again.

But about 2 days ago I noticed idle became more rough, not that you can see dash and seats shudder but still you can feel vibration in the steering wheel and the gas pedal. Then today when I was on the freeway doing 80 and holding the gas pedal in the same position the RPM started to dip and wasnt reacting to gas pedal for a few seconds as if the fuel wasn't properly injected. I had this a couple of times on the freeway tonight especially on high RPMs but didn't have it once on the street while doing 35... My first thought was spark plugs but I just wanted to confirm it with you guys because I wouldn't be able to change them alone so thats probably gonna be expensive, what are the other options?

There's also one more thing, I have a problem with coolant leak, so far I was adding half a gallon every week, and I get a white cloud from the exhaust when I start the car, I thought it was a head gasket but the oil seems to have no water in it at all and there are no leaks under the car... So I'm kinda frustrated here too. Also the temp gauge might be lying but I'm not sure about that, thermostat has been taken off long before me, and right now I'm afraid I overheated the engine a couple of times and all this rough running thing might be the first symptom the engine is dying. What do you guys think?

Oh yea, forgot to say it takes about 3 seconds to actually start the car when its warm, when its cold it starts right away...

 

Have you scanned it for codes? Have you checked the fuel pressure?

He replaced what black plastic thing further along the manifold? The IAC is on the bottom of the throttle body. The throttle position sensor is right above it on the throttle body.

Courtesy of Shobox:

http://shbox.com/1/tps.jpg

The only way to correctly adjust the idle on a 95 LT1 is by programming the PCM. Does your mechanic have that capability, or did he just start playing with the throttle stop screw, possibly throwing the IAC counts and the TPS voltage off.

 

Thanks for the link. Sorry my bad, it was TPS and MAC that were replaced, the mechanic just messed with the throttle screw without any electronics involved. I'm looking for a place to scan it for codes in my area but so far no one had the right equippment, BTW does anyone know of a good Camaro mechanic in LA area?

 

Just curious...why do you have a Russian-based e-mail address?