Hello,

Im new to the camaro scene and would really like some advice. Last week I purchased a 1994 Z28 with 68,000 miles on it. The car is stock as of now, other then Flowmaster exhaust. After the car is running about 30 mins or so. It begins to miss alot and idle very ruff when sitting still if the car is in gear. The check engine light never comes on. Car had a full tuneup 3 months before I purchased it. The temp was a little warm so I replaced the thermostat this morning. It's still doing the same thing. Has anyone ever had this happen before? Any help would be greatly appreciated..thanks

Chris

 

1) Replace ignition wires
2) Replace spark plogs with factory issue, do not change brands
3) Replace engine temperature sensor
If above fails:
4) Replace optispark and water pump. If water pump leaks it will kill optispark, so it pays to do them both at the same time

 

thanks for your quick response!! the plugs and wires are 6 months old, The water pump is 1 yr old. do you think I should do them again anyway?

 

Plugs should still be good if you used stock ones. Wires should still be good unless they got burned or have internal breaks.
Have you washed your engine recently? If water got into the optispark, which is very easy, you may have to replace it, or at least the cap and rotor (MSD has a good replacement, GM only sells the whole assembly). You can try the engine temp sensor first, not to be confused with the temp gage sensor, as it is cheap compared to the optispark.

 

hey z28pete, thanks for all of your help....I was just outside and doing some playing around..Im not trying to sound like an idiot but i have a question for ya..There is a little black sensor on the intake, about 1 inch wide and 2 inches long..has 3 wires going to it..if i unplug it..the fans kick on and the temp goes to 170 and the car runs great.do you know what that sensor is called? and if so...would that be what my problem is?

 

That is the air temp sensor. it is used by the computer to adjust fuel mixture and timing to compensate for changes in intake air temp. If you unplug it you should get a check engine lite, and cause the engine to go into "Open Loop Mode" You can run with it unplugged and nothing bad will happen. Try running with it unplugged until the engine is good and warm. If it still runs good it means your ignition and injectors are working OK.

When you are running in "OPEN LOOP" most sensor inputs are ignored by the computer, which means you have a bad sensor somewhere. Your job is to figure out which one is bad without changing them all. Apparently the bad sensor is sending erroneous data, but it is not broken, so the check engine lite does not come on. You may want to change the Air Temp Sensor as this is the easiest one to get to, and then the Engine Temp Sensor on the water pump. Or maybe the O2 sensors, but not likely. You can also get a scan tool and see what each sensor is sending out and if it is unreasunable that sensor may be bad.

Also check that the check that the check engine lite works, when you disconnect the Air Temp Sensor, the trouble lite should come on within a minute. If it doesn't it may be burned out and hide trouble codes. If the lite fails, then you will need a scan tool.

 

Hey I have the same problem! I own a 94 z28 too. mine hasnt been tuned either but I am going to do it very soon. Did yours ever stall out cause it idled hard? Mine only seems to do it after it rains and the car underneath gets wet or if I wash it. Weird!!

 

Welcome to the Opticrap Distributor, and all the crap that happens once it gets wet.

 

Not sure if this helps- I had a similar problem with my 1995 Caprice (LT1 engine). Turned out to be the EGR valve was sticking due to carbon build-up on the pintle (shaft). Locate the valve at the rear of the motor with a mirror. Unplug the vacuum line to it and restart the motor/ go for a short drive. Misfire gone? Valve is carboned up. Do not drive too long with the valve disconnected, the engine needs the dilution of exhaust or it will ping and will run noticeably hotter than normal. Remove valve using a small mirror and an open end wrench. Leave the gasket alone for now. Test the valve by squeezing the pintle upwards. If it binds or offers a lot of resistance it is definitely in need of cleaning. Even if it is OK, spray it with carb cleaner/ decarbonizer until it moves freely. It is definitely serviceable. Left alone the pintle can seize so badly that it snaps and your vehicle will run terribly all the time. Reinstall and hopefully you are good to go. A new valve is 85-100 bucks Canadian- service it first!

 

Good point andy mac, a fouled up EGR will definetely result in a sick running engine.