Hello All...
I am new to the forum and looking for some help. I have a 92 z28 1LE. I changed the spark plugs about 2 months ago. After driving it a little while I noticed after it warms up the idle is rough. It idles in neutral around 1500 rpms(what the guages read may be wrong) then drops to about 900-1000 rpm and kicks back up to 1500. It has stalled a couple of times but I turned up the idle so now it doesnt stall.. Let me start by saying what I have done.

Replaced spark plug wires
Replaced idle air control valve
Replaced throttle postion sensor
Replaced distributor cap
Blocked off the egr valve
Plugged the smog pump hose which has vacuum as I dont have one

If anyone has any ideas or suggestions of what it could be please let me know. I am out of ideas...

Brent

 

See what your true rpm's are by hooking up an aftermarket or tuning tach (if you have one). These 1990-92 tachometers are notorious for lying to you. My 91 read double of what the engine really was at, and if you do an online search you'll find what an epidemic it is. Your issue may just be that the engine is idling slower than you think it is, and naturally it's going to stall if the rpm's are too low. By the way, how did you "turn up the idle"? Here's some reading material on the factory tach: http://www.thirdgen.org/techboard/el...eter-fix.html?

 

I will try hooking the tuning tach up to it. My worries is even when I turned it up til you could hear it idling higher it was still dropping about 500 rpms. I used the screw thats next to the throttle body to adjust the rpms. The only thing I can think of is since it was after I changed the spark plugs is that it was bad plugs. I would imagine though it would run poorly all the time and not only when it warms up at idle.

 

did you set the voltage on the tps after installing it? that is critical in preventing an idle hunt

 

Should not use the throttle valve stop screws for adjusting idle speed, these are factory preset. Idle speed is controlled by the IAC valve, and if the throttle stops are not set properly, the IAC will have problems in holding the idle speed. Was the car idling properly before the plug change? If it was, then you need to check your work, as the rough idle may be due to a misfire problem. Also, as Micro said, check the voltage on the TPS and make sure it is set to spec.

 

Voltage on the TPS should be very close to .5 at idle, 5 at WOT. I played around with all of that stuff on mine and gave up and went carbed when I put in a 350 haha

 

When everything else fails, read the instructions or put in a carb. lol