Help! what do i need

[drudge86]

i bought a 86 and it surges when it getd warm the man i purchased it from said a mild cam was installed and thats why it does that what do i purchase to fix this? A chip?

 

[aklim]

Dunno. You have an unknown cam and you don't seem to know whether the chip was tweaked or not. Can you find out info on both? It MIGHT be as simple as setting the IAC but it could be more.

 

[drudge86]

i asked him if he had the cam card or reflashed the computer or added a chip and he said no. he said its one step up from stock and i have driven alot of latemodel stock cars and its no lope or twang to the cam so im guessing its really close to stock. now if i give it a little gas it idles perfect i tried to turn the idle up a little and it did not help

 

[drudge86]

hey no chips or reflashing of the computer

 

[Schrade]

Vacuum leak?

Originally Posted by Schrade
No one got the proper technique for vacuum leak detection... :confused

FIRST (fully warmed up motor); block the pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' already from a vacuum leak, you ain't gonna' find any vacuum leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.

AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, until you get the SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vac leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-huh).

If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot.

Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.

Bookmark this post YUP.

 

[vetteoz]

i tried to turn the idle up a little and it did not help

The proper way ?
Corvette Action Center Knowledgebase :: 1985 - 1991: Technical Article: How to Adjust your Early C4 TPS and Idle Speed

i he said its one step up from stock

Could be a problem not related to the cam ; bad IAC , blocked IAC passages , etc.
As noted in link above , pull TB dis-assemble and clean out.Lotta gunk gets in there over time blocking thing up

 

[vetteoz]

Vacuum leak?

Doubtfull.
Vac leak usually shows up as a higher than wanted idle speed that can't be tuned out ; rather than intermittent surging
With a BIG cam on stock tune for example; the ECM is controlling the IAC to bring idle down to it's programmed idle speed that the engine won't run at ( because of the cam ) so you get constant rev surging