View Full Version : HT 4100 fast idle after switching throttle body: NEED HELP!

NY Cap District CLC
10-03-10, 09:56 PM
So my cousin's '82 Fleetwood with HT 4100 had a problem where the butterfly linkage in the throttle body got corroded (from sitting) and was stuck at idle. So, we took the throttle body off the car, was able to free up the butterfly, but decided to put a spare throttle body on the car. After starting it up, it is idling very fast (probably over 2000 rpm's). Then switched back to the original, but it still idling fast. Check engine light on (codes 26 short circuited Idle Speed Control, 27, 52 ECM reset). Prior to this the car idled fine.
So I tried switch the Idle Speed Control unit (same problem). If fact, I had to remove the screw that the butterfly linkage rests on as the idle was even faster with it in. Not sure what went wrong. Could it be throttle position sensor or vaccum leak?
Otherwise the car runs great, no hesitation or smoke. Any suggestions out there?

10-03-10, 10:17 PM
TPS, I will guess.

Robin Banx
10-04-10, 12:12 AM
On an 81 car the engine should be a 368. If you disconnect the ISC motor, there is a set procedure for reconnecting it. You should get a code 30 on diagnosis also. The engine will idle in excess of 1200 rpm and continue posting code 30 until the ISC motor is reconnected correctly. I am having this issue with my 81 right now. If you are working on a 4100, it will be a newer car, not an 81 and I'm not sure that the codes and procedures are the same. You will need access to a 4100 service manual to do the reconnect properly.

Hope this helps............R.

10-04-10, 12:50 AM
The service manual has three conditions that cause these codes. Defective throttle switch, defective wires and terminals and an ECM which is unable to process signals properly. I think its the throttle switch because code 26 means its reading closed, code 27 means its reading open.

10-04-10, 04:24 PM
Maybe it's an 81 with 4.1 V6?

NY Cap District CLC
10-04-10, 07:49 PM
Sorry, I meant '82 (typo) but appreciate the advice.

NY Cap District CLC
10-04-10, 07:50 PM
Is the ISC motor the idle speed control motor that retracts the screw? Should I check voltage to it after screw is retracted?

Robin Banx
10-04-10, 09:35 PM
No...... See section 6D3-12 of your Service Manual re ISC motor adjustments. If you don't have one and I feel like a lot ot typing later on I will quote the section to you. But don't mess with the ISC motor until you have read the manual.


NY Cap District CLC
10-05-10, 01:43 PM
Robin, I have the service manual and will check Section 6D3-12. It's funny that retractable screw in ISC motor is "E" whereas the spare TBI (from same year Fleetwood) is "L". corresponding to different measurements. Thanks for input.