Throttle Body Problem
Thread Starter
Drifting
Joined: Aug 2002
Posts: 1,773
Likes: 123
From: Birmingham AL
Throttle Body Problem
On my '89 L98 with the ZF6, I have an issue with the idle after pushing in the clutch when driving. I crank up the car and it idles fine at 700 rpm. When I drive and push in the clutch, the idle is high at about 2000 rpm. I tap the throttle and it goes back down to 700. It happens every time. I just rebuilt and cleaned the throttle body. I set the butterflies to where they close without binding. And I did set the tps voltage to .54. I even threw a new tps on there and it does the same thing. It didn't do this before the rebuild. Any ideas? Maybe I ruined the IAC when wiping the pintle off? I'm not sure why it would be the IAC if tapping the throttle returns it to idle and it does idle smoothly. I checked the butterflies after it hung up at 2000 RPM and they were closed (not binding). There is no slop in the butterfly shaft at all. What gives? Do I need to lube the shaft bearings? Any help would be much appreciated. Thanks
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Is the Vette moving when you push in the clutch or are you stationary? From reading your post it appears you are moving. I cannot understand why tapping the accel will reduce the idle whether you are sitting still or moving. If you are moving, the ECM will see the speed and kick up the idle......this is what happens on my 89.
Drifting
Joined: Apr 2005
Posts: 1,278
Likes: 12
From: New York
Do you have a scan tool? If so hook it up, and see what the step count is on the IAC when this happening, is it changing? When you rebuilt the throttle body, did you remove the IAC? When you put it back together, did you follow the FSM for resetting this. Turn the ignition on, don't start, wait a moment, then off, then start the car.
Thread Starter
Drifting
Joined: Aug 2002
Posts: 1,773
Likes: 123
From: Birmingham AL
Yes, I did follow the procedure for resetting the IAC. I will hook up my scan tool and check the IAC counts this weekend. Wow, this problem makes the car a bit aggravating to drive. I can't understand why tapping the throttle brings it back down if it is not a mechanical linkage or binding issue. Apparently it's not a tps problem either as I swapped that part. It will do the same thing either while rolling or at a stop. The car just screams until I tap the throttle. In fact I can only drive so slow as the motor seems to never want to go under 1600 or so rpm after accelerating. Thanks for the replies.
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Anthony: Do you have the cruize control on this car? If so, have you tried to disconnect the cruize control cable (from the TB) or disable this function on your car? This may be a factor in your problem.
Le Mans Master
Joined: Aug 2004
Posts: 5,141
Likes: 7
From: Metairie Louisiana
Check the wiring harness that plugs into the TPS sensor. Mine did almost the same thing as yours. I also tried a new TPS with no luck. I was also getting the correct voltage. It was intermittent at times and the throttle/idle was sticking. It was shorting out at the harness due to a loose wire where the nitrous was tapped in at. A new harness from the dealer was around $40 I think.
Last edited by rickneworleansla; Oct 20, 2006 at 11:35 AM.
Instructor
Joined: Oct 2005
Posts: 143
Likes: 0
From: Lincolnshire,ENGLAND
I had this exact same problem on my '91 ZF6 after a TB clean up. I checked absolutly everything, even went through 2 new IAC valves and a new bbk trottle body-still same problem
In the end i figured it must be the IAC bore in the TB coolant passage plate as i used my old one with the new bbk TB and new IAC valve.
Bought a new coolant passage plate cheap off ebay- idle has been right ever since.
Not saying this is definatly whats up with yours,but its the only thing that worked for me.
In the end i figured it must be the IAC bore in the TB coolant passage plate as i used my old one with the new bbk TB and new IAC valve.
Bought a new coolant passage plate cheap off ebay- idle has been right ever since.
Not saying this is definatly whats up with yours,but its the only thing that worked for me.
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Thread Starter
Drifting
Joined: Aug 2002
Posts: 1,773
Likes: 123
From: Birmingham AL
Well, it turned out to be that the throttle body bushings needed a little lube. I ran the car for a while until it started sticking and it was the bushings in the throttle body. There is no slop in any direction and not any binding when cold, but when running the butterflies would not close completely. I sprayed some lube into the bushings and it runs perfectly. I guess that the tb cleaner removed any lube that was there before.
Drifting
Joined: Oct 2006
Posts: 1,694
Likes: 0
From: Beaverton Oregon
My '86 L98 does this same thing - fluctuating idle while driving, anywhere from 700 to 1800. If I tap the pedal, it goes away. If I lift the peddle with the top of my foot, it goes away. Guess I'll spray some Silicone Lube in there today - thanks for the tip.