Recently my 1987 IROC 5.0 liter, 5sp engine started to run rough and the tachometer has been going crazy. When the car is idling (seemingly smooth)the tach is jumping all over the place, going from 500rpm to 1500 rpm while hovering around 750rpm (recommended idle speed). Then when I accelerate the car bucks and misses until I floor it, and finally its runs relatively smooth. But, the minute you back off the throttle it starts to miss badly again (does this in all gears). I should mention that I have replaced the coil wire, PCV valve, tried fuel injector cleaner and haven't found any short yet. Does my problem sound familiar to anyone??
My engine has 170k on it and I replaced the computer about 2 years ago.
Thanks for any replies.

 

Sounds like some kind of ignition problem. Have you checked the coil itself?

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L98, stock 3.27s, Hooker shorty headers, custom 2.5inch Y-pipe, no cat, 3inch 2chamber flowmaster, JET AFPR, Ported MAF, Best ET: 13.86 @100mph. 1.99 60'
17 inch ROH "ZS" wheels. 17x8.5(front) and 17x9.5 (rear). And just recently T56!

 

check your plug wires. my car did this a couple of times. once, one of the wires was cooked on the header. once it was the cap posts were so wore out it did the same thing you described. if that is it replace it with a good ones. Accel or something...

 

o2 sensor

 

That's how my IAC problem started. Although I didn't get the bucks and misses when accelerating. Try adjusting your IAC to see if that helps and check if it's dirty.

Hope that helps

[This message has been edited by Drowned (edited October 19, 2000).]

 

More Info: Thanks for the help everyone. Could it really be the O2 sensor as someone suggests? I have already checked the engine codes and a "21" and "22" appeared. I replaced the TPS and nothing changed. Wouldn't I get a code for the O2 sensor??

 

Hmmmm, I got codes 21 and 22 a few days ago cause my TPS was bad and the car would feel like it was running out of gas. The car would show me a SES light and a few mins later the car would start going crazy. I would just turn it off and start it up again and it would be fine. The problem would start again a few mins later though. All this because I had a bad TPS... and it was BRAND NEW!

You should try adjusting your TPS, it might help, although my problem stopped until I got a new TPS

[This message has been edited by Drowned (edited October 19, 2000).]

 

That sounds similar to my problem, 5.0 tpi 5 speed, won't idle cold, throttle response is horrible until you floor it and get into higher rpms. No codes, but i think it's IAC since when i disconnected it idle was at 1500 rpms and i got my throttle response back but lost overall power big time. I also get a hissing sound(sometimes it's not constant) coming from around the throttle body.

 

My car did most of that once. I replaced the rotor, cap, and wires. I haven't had a problem since. It seems too simple to work, but it did the trick.