bad idle UP and Down

[buickshake87]

My, stock, 87 gn is reving up and down when i start it, sometimes to the point of quitting. Almost like its loading up, but once this thing gets warm it gets much better. Like clockwork when I lightly press the gas the damn thing will miss and then run out smooth.. say i'm in overdrive cruising 70 trying to maintain speed type of throttle position will make it kinda hick up but if I give throttle clears up completely and if Im off the gas its smooth also, just that point of touching the throttle is where the problem acts up.. This thing is driving me crazy... tps? iac? something little but I can't figure it out... if you guys can help I would love it...

Chris

 

[mikestertwo]

Could be a lot of things. Bad O2 sensor, vacuum leak, misadjusted IAC or TPS. Any scan tool readings?

 

[1fast6]

could be maf

 

[buickshake87]

Thanks and I know its hard to tell without looking or being here, I have replaced all vacuum lines and few other things... egr maybe? also... how can i test maf? Thanks for the help ...

Chris

 

[1fast6]

Thanks and I know its hard to tell without looking or being here, I have replaced all vacuum lines and few other things... egr maybe? also... how can i test maf? Thanks for the help ...

Chris

best way is with a known good one. If you don't have one then you can smack on it with the handle of a screwdriver. if the idle changes then it's bad.

 

[87gninpa]

When the car is running, tap the maf and see if it stumbles. If so, its bad but if not, it still could mean bad MAF. You can also unplug it and see if it clears up. FWIW, I had a very similar issue a couple of months ago and it turned out my fuel pressure gauge was reading almost 10 psi high, Put a different gauge on, bumped the fuel pressure up to ~ 43 line off and its been great ever since.

 

[GullsGN]

How stock? If you are still running wih the original factory chip you need to change it. The factory chip has horrible idling characteristics. If you still have the original MAF that would be my first suspect.

 

[bmackinnon]

if it runs fine when you nail it, it's (probably) not the maf... if it has the stock chip, it is hard to tell... they idle like crap at cold start... mine always died at least once, even when new... very light throttle with the stock chip was not great either... hiccups were very common. Obviously, if you want to really be able to diagnose it, you need a scan tool to observe the relevant parameters when it's acting up. Suggest a modern chip (if it's not already) and see where that gets you...