I just swapped in my Crane Powermax (formely CompuCam) 2031. This is supposed to be a cam that is compatible with the stock computer, however my car now idles steady at about 2500 RPM. The idle is not erratic at all, in fact it seems like the car wants it to be that high. I'm assuming I have lost some idle vacuum and that is throwing the computer off via the MAP sensor, but how can that be when this cam is designed for use with the stock chip? I even called Crane and asked if this cam would work for a TBI car, and they said it would. I was told idle vacuum would be between 15-16 inches, does anybody know what the idle vacuum is on a stock 89 5.0 TBI engine?

Any ideas are appreciated.

BTW, I am running a Jet Stage II chip, but I don't see how that would cause any negative effects following a cam swap.

For any of you who are interested, the car now sounds quite a bit louder than before. I love the new sound it has, however I haven't had a chance to check for performance gains.

The car is also fitted with Edelbrock headers flowing into the stock cat and followed by a Flowmaster 3" cat-back.

Any help is appreciated,

Jason

 

Sounds like there is a vacuum leak somewhere. Do you have an ALDL scanner?

It's getting air from somewhere it shouldn't otherwise it would not be able to hold a steady 2500 RPM idle. Check around the intake gaskets with brake cleaner. If you have a scanner, check your IAC counts.

 

No, I don't have a scanner or anything like that. Tomorrow I'm going to disconnect the IAC motor before start-up. This should leave the IAC in the park postion and prevent the engine from getting much air. If there is no vacuum leak, the car shouldn't run, or at least at a very slow idle speed.

Depending on the results of that, I may get a vacuum gauge and see if I can read what the idle vacuum is.

It would seem to me that if the ECM is programmed to keep a certain idle speed and the car is idling too high, that the ECM would close off the IAC to try and bring the idle down. If this is correct, disconnecting the IAC should have little effect on my current idling problems. Then I would know it's a vacuum leak.

However I was under the impression that a vacuum leak caused a surging or unstable idle. Is this correct? My idle is rock solid at 2000-2500 RPM.

Jason

 

No, a vacuum leak is just going to cause a high idle. Another way to check is block off the TB with the car running, it should die in short order. If it dies, check the TPS setting. Oh yea, and make sure the cruise control cable isnt binding if you have cruise, that will do it too. Sometimes it will hang up on the end where the diaphragm is.