First off let me say hello and thanks for allowing me into the forum. I am a long time Buick owner, and have raised my kids to be Buick owners too. I am writing looking for assistance with a problem on one of our cars. Currently I own a 56 Super, a 69 GS 400, a 69 Electra, and my wife of 35 yrs owns an 06 Lacrosse. One boy owns a 93 Regal GS, another a 93 Regal Custom and the last an 89 Lesabre T type as well as an 03 Regal LS. I don't want to go into the list of Buicks we owned and let go now, but maybe later.
While we have none of the "go really fast" Buicks currently, we still can appreciate those cars. And the problem we have is with a derivitive of those cars, so we are praying someone here can offer a possible solution to our eratic idle in the 89 Lesabre T.
This car is still basically stock with 200K on the whole car except the engine which has roughly 160K on it. We changed the original engine out two falls ago and have had this problem ever since. The car we got the engine out of was another 89 Lesabre T type, and we drove it here. It did not have this problem. The old engine did not have this problem.
Before installing the replacement engine we put in a new timing chain and gear set plus a new tensioner and cam shaft magnet. We also changed the throttle body with new gaskets. Prior to putting this engine in we changed the computer using the original prom because the old engine was having problems starting quickly. That computer and prom set up was used for over 2,000 satisfactory miles with the old engine.
So here's the problem detail:
The car starts right away as it should. But within seconds while still on fast idle it fluctuates about 300 RPM faster to lower. It should idle when warm at around 800 RPM. It will drop to 500 rpm and return to 800 RPM several times per minute. It will feel like it's about to stall sometimes and then catch up and resettle to 800 and then continue to fluctuate. Off idle and on the road under power you can't feel the fluctuation but it's still there. Still the car drives beautifully shifting correctly and with expected response and power.
We have thrown a lot of sensors at this thing prior to our last mechanic's diagnosis. Throttle position sensor, Idle air control, Mat Sensor, Mass Air Flow sensor, Oxygen sensor, the entire wiring harness from the car the engine came from. Crankshaft sensor, and cam sensor. We put in a used EGR valve from another car that we know was working moments before we got the part.
We have taken this car to several mechanics and the last one who is considered very good with GM's of this era used his scanner said this appears to be a vacuum leak, not sensor or computer driven. All the sensors were functioning within acceptable parameters ( a good thing considering the cost). He did say, however, that he suspects the timing may be off by one tooth. He qualified that by saying he only thinks that because we said the engine ran good before coming out the other car and we changed those parts.
He found a leak at the vacuum tower but he said he did not think that was going to be the sole fix. We replaced the vacuum tower gasket and checked the tower for obvious leaks. When we did that we also took off all the vacuum lines and then blocked all the vacuum ports and still had the bad idle.
At this point I am wondering where else we may have a vacuum leak or if anyone else experienced a similar problem and may have a possible solution? Any help would be greatly appreciated as this thing is driving me nuts.
BTW, we did a compression test in the process of diagnosis and found all 6 cylinders in the 151-155 lbs range. The engine does not burn oil.
Thanks for the read.
John De Fiore
While we have none of the "go really fast" Buicks currently, we still can appreciate those cars. And the problem we have is with a derivitive of those cars, so we are praying someone here can offer a possible solution to our eratic idle in the 89 Lesabre T.
This car is still basically stock with 200K on the whole car except the engine which has roughly 160K on it. We changed the original engine out two falls ago and have had this problem ever since. The car we got the engine out of was another 89 Lesabre T type, and we drove it here. It did not have this problem. The old engine did not have this problem.
Before installing the replacement engine we put in a new timing chain and gear set plus a new tensioner and cam shaft magnet. We also changed the throttle body with new gaskets. Prior to putting this engine in we changed the computer using the original prom because the old engine was having problems starting quickly. That computer and prom set up was used for over 2,000 satisfactory miles with the old engine.
So here's the problem detail:
The car starts right away as it should. But within seconds while still on fast idle it fluctuates about 300 RPM faster to lower. It should idle when warm at around 800 RPM. It will drop to 500 rpm and return to 800 RPM several times per minute. It will feel like it's about to stall sometimes and then catch up and resettle to 800 and then continue to fluctuate. Off idle and on the road under power you can't feel the fluctuation but it's still there. Still the car drives beautifully shifting correctly and with expected response and power.
We have thrown a lot of sensors at this thing prior to our last mechanic's diagnosis. Throttle position sensor, Idle air control, Mat Sensor, Mass Air Flow sensor, Oxygen sensor, the entire wiring harness from the car the engine came from. Crankshaft sensor, and cam sensor. We put in a used EGR valve from another car that we know was working moments before we got the part.
We have taken this car to several mechanics and the last one who is considered very good with GM's of this era used his scanner said this appears to be a vacuum leak, not sensor or computer driven. All the sensors were functioning within acceptable parameters ( a good thing considering the cost). He did say, however, that he suspects the timing may be off by one tooth. He qualified that by saying he only thinks that because we said the engine ran good before coming out the other car and we changed those parts.
He found a leak at the vacuum tower but he said he did not think that was going to be the sole fix. We replaced the vacuum tower gasket and checked the tower for obvious leaks. When we did that we also took off all the vacuum lines and then blocked all the vacuum ports and still had the bad idle.
At this point I am wondering where else we may have a vacuum leak or if anyone else experienced a similar problem and may have a possible solution? Any help would be greatly appreciated as this thing is driving me nuts.
BTW, we did a compression test in the process of diagnosis and found all 6 cylinders in the 151-155 lbs range. The engine does not burn oil.
Thanks for the read.
John De Fiore
