High Idle , Thermowax , TPS
01-17-10, 08:37 PM
#1
High Idle , Thermowax , TPS
For anyone out there who might be having a similar problem, hope this helps.
I had a high idle problem. When I started the car it would rev to 3K, then slowly drop to 2K. Then after warming up it would idle at 3K again. I checked all the obvious things, TPS, BAC, solenoids, etc. I thought the TPS was bad but I think the specs in the FSM are wrong for the A-C at WOT. Using a home-made test light I was able to set the TPS.
The problem turned out to be a plugged coolant line going to the thermowax. Though the thermowax operated to spec it was not getting warm coolant to move the fast idle cam and to fully open the double throttle. This was acting like a choke when the engine was warm making the idle go even higher. As soon as I replaced the coolant line the fast idle cam moved and the double throttle diaphram operated as it should giving me a perfect idle.
I had a high idle problem. When I started the car it would rev to 3K, then slowly drop to 2K. Then after warming up it would idle at 3K again. I checked all the obvious things, TPS, BAC, solenoids, etc. I thought the TPS was bad but I think the specs in the FSM are wrong for the A-C at WOT. Using a home-made test light I was able to set the TPS.
The problem turned out to be a plugged coolant line going to the thermowax. Though the thermowax operated to spec it was not getting warm coolant to move the fast idle cam and to fully open the double throttle. This was acting like a choke when the engine was warm making the idle go even higher. As soon as I replaced the coolant line the fast idle cam moved and the double throttle diaphram operated as it should giving me a perfect idle.
01-17-10, 10:30 PM
#2
Assuming the TPS is good and set properly, narrow range signal will be over 1 volt with the fast idle cam opening the throttle, probably like 1.2-1.4 volts. When fast idle is disengaged, voltage should be 1 volt or less.
In the OP's situation you should be able to rotate the fast idle cam away with your finger and the idle will drop down. You can do this by rotating the arm which has the screw touching the top of the thermowax rod.
In the OP's situation you should be able to rotate the fast idle cam away with your finger and the idle will drop down. You can do this by rotating the arm which has the screw touching the top of the thermowax rod.
01-18-10, 12:11 PM
#3
The voltage readings you are refering to are measured by backprobing terminals A-C with the engine running?
I'll double check these just to make sure I have this right. Using the test light, I was a little unclear as to whether to set the single light on when the engine was warm (fast idle cam disengaged) or cold (fast idle cam engaged) 'cause best I can tell it does make a difference.
The possible typo in the FSM that I'm referring to is the resistance value of 5 kohms between A-C at WOT.
Yes, rotating the fast idle cam away and having the revs drop was how I first detected that something was wrong with that system. When removing the thermowax to test it I found that the lines were mostly dry and when I tried to suck the crud out of the lines (back flush) with a vacuum pump I realized that one of them was completely plugged. Specifically it was the short aluminum line that screws to the BAC that had completely corroded inside and closed itself off.
One more thing... the long debated 3800 rpm hesitation. Mine was never severe, just brief and subtle. Now I think it's gone completely, at least I could not feel it on my drive in to work this morning. In general the car runs much smoother too. So could the 3800 hesitation be related to the TPS adjustment, the fast idle cam, or the double throttle that was not opening when warm? Hmmm... Possible things to check if you are having this problem.
I'll double check these just to make sure I have this right. Using the test light, I was a little unclear as to whether to set the single light on when the engine was warm (fast idle cam disengaged) or cold (fast idle cam engaged) 'cause best I can tell it does make a difference.
The possible typo in the FSM that I'm referring to is the resistance value of 5 kohms between A-C at WOT.
Yes, rotating the fast idle cam away and having the revs drop was how I first detected that something was wrong with that system. When removing the thermowax to test it I found that the lines were mostly dry and when I tried to suck the crud out of the lines (back flush) with a vacuum pump I realized that one of them was completely plugged. Specifically it was the short aluminum line that screws to the BAC that had completely corroded inside and closed itself off.
One more thing... the long debated 3800 rpm hesitation. Mine was never severe, just brief and subtle. Now I think it's gone completely, at least I could not feel it on my drive in to work this morning. In general the car runs much smoother too. So could the 3800 hesitation be related to the TPS adjustment, the fast idle cam, or the double throttle that was not opening when warm? Hmmm... Possible things to check if you are having this problem.
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