I have an 86 transam..

It has a rough idle when the car gets warm and on the freeway, if i keep a steady cruise...i can barely feel the car getting a little power and then losing a little power...lasts about 5 seconds intervals...

no codes...what could be the problem??

gary

 

The ECM is designed to allow a regular oscillation from slightly rich to slightly lean. It doesn't hold the mixture at a perfect and steady 14.7:1. This is done for the benefit of the 3-way catalyst. When it cycles rich, that keeps the platinum part of the cat happy. When it cycles lean, that keeps the iridium part of the cat happy. Up and down, rich and lean, all the time.

Now, certain assumptions are made when this is all going on. The ECM was programmed to assume that EGR would be available, that the charcoal cannister system is working, that the PCV is working, that the carb is working, that the various sensors are working. There IS some fault tolerance, but I'd wager that it is least tolerant when the EGR is not working.

If I were you, I'd pull the carb and EGR valve off and look for a lot of carbon build-up. I've been there. I found it plugged with soot and cleaning that all out made the difference!

 

If this is a carb car, it needs a carb rebuild. That's the symptom of a lean condition, which usually results from garbage accumulating in the fuel passages in the carb.

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"So many Mustangs, so little time..."

 

it's a TPI car...i recently put a new 350 in...witha cam and it's got a custom chip...

i'm thinking it is the EGR because that's pretty much the only part i didn't change...

the thing is, there's no check engine light...should there be one...?

thanks

 

I based my answer that it was bone stock. I would have to make an educated guess that your injectors are too small to deliver the fuel that the O2 sensor is calling for. The ECM and performance chip can call for the fuel but if your fuel pump or injectors can't deliver, then you'll get that leaned-out sensation you've described. I'm not sure how EGR figures in with those hi-po chips. I could very well be that the chip maker assumes you've DISCONNECTED the EGR. That's something you'll have to ask from the company that made the chip.