1991 Cadillac Brougham Rough Idle and Stalling

Tiny
JGROFF05
  • MEMBER
  • 1991 CADILLAC BROUGHAM
  • V8
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
My car is a 1991 cadillac brougham d elegance v8 305 5.0L. My probelm is this. I will drive on the highway and it will drive fine. Here is the kicker if I go above speeds of 58 what happens is when I come to slow down to a stop my car will start idling real rough and will almost stall out. My probelm is I cannot find what is causing this. I got no check engine light and I cannot find a solution. I have checked every vacuum line and have no leaks. I have replaced the EGR valve, the TPS sensor, the catalytic converter, the IAC motor and still cannot find the problem. I have prot injection and the jets are spraying fine into each chamber of the throttle body and there is no problem with fuel. I am stumped and cannot figure this out. This has been going on for months and I would like to be able to drive my car at high speeds again and not worry about it stalling out. Please help me if you can I am in need of it.
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Monday, December 7th, 2009 AT 5:53 PM

3 Replies

Tiny
BUDDYCRAIGG
  • EXPERT
That really sounds like a lock-up torque converter staying locked up.
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Tuesday, December 8th, 2009 AT 1:23 AM
Tiny
JGROFF05
  • MEMBER
Before I go into the tranny and try that I forgot to mention this to you. Here is another wrench into the mix. I would put fuel injector cleaner into my tank and I could drive freely at any speed and I would not experience any of the problems but when I run gas without the cleaner in it that is when this rough idle problem occurs problem occurs. I use STP fuel injector cleaner and that allows my car to run at high speeds without messing up when I come to a stop.
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Tuesday, December 8th, 2009 AT 8:22 AM
Tiny
BUDDYCRAIGG
  • EXPERT
I've been thinking about your new info all day and my hurd hets, I mean my head hurts.

It's not like we are in a back to the future movie where "when this baby hits 58 MPH, watch out."

These are the two things that I can think of before my head explodes.

1, the EGR valve is opening up and not closing fast enough. (You can disprove this by running with your EGR unplugged for a few days)

2, you have high compression from carbon build up and are getting detonation after a lean cruise on the highway. (You can disprove this by running the fuel tank almost empty and then putting in a 1/4 tank of premium octane)
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Tuesday, December 8th, 2009 AT 11:50 PM

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