87 with errratic idle

[RonV87]

I have an 87 L98 automatic with 65000 miles that frequently goes up and down between 600 and 900 rpms at idle. More noticeable with the A/C on. Pretty annoying when stopped at a light with foot on the brake. The books say look for a hose vacuum leak, clogged pcv valve, head gasket leak, bad plugs, etc. I can't seem to find anything wrong. Any suggestions on what to look for to narrow the search down? Any help is much appreciated.

RonV87

 

[reynald leclerc]

hello, i had the same problem, on my vette 87, and i saw that i had an escape on the trotle body(the gasket is cut)and more the tps was put out of order, also oxidation spark plug, if that you to help has resoudre your problem

 

[pthoma1]

Never had this problem, but i supose it could be the TPS doesn't really seem likely if it is driving fine.

 

[jsinga]

Of course a scan tool will tell you if you have an erratic TPS. You could have a problem with the IAC (Idle Air Control). It actually controls idle speed. Try cleaning the trottle body. Try unplugging the IAC and see if the idle is stable. It should idle around 500rpm with the IAC disconnected if minimum idle is set properly.

You may have to take the IAC out to clean it good.

JS

 

[TerryD]

Check belt tensioner, and if its jumping a little, it might couse the surging