3.2 Idle Problem

[Rot 911]

Just finished coming back from the 50 mile test drive after the rebuild. Everything is looking and running fine except for one thing. The idle is setting at 850 rpms which is ok. However, sometimes the idle will jump up to 2000 rpm and stay there for a minute or so and then drop back down to 850 again. And when I was driving sometimes the rpms would drop when I was shifting and sometimes they just stayed high between 2000 and 3000 rpms. I checked and the linkage is not binding or hanging up. In fact the idle would jump up to 2000 rpms even with the linkage disconnected. And ideas? On the rebuild I replaced both the speed sensors and the TDC sensor.

[Steve W]

Kurt, you could check that your idle microswitch on the throttle body is engaging properly. I've seen where an old switch with a rotted rubber seal would cause the switch to 'hang'. If it doesn't close, the idle will be high because the DME doesn't know to have the idle valve lock it down to idle.

[Rot 911]

Originally posted by Steve W
Kurt, you could check that your idle microswitch on the throttle body is engaging properly. I've seen where an old switch with a rotted rubber seal would cause the switch to 'hang'. If it doesn't close, the idle will be high because the DME doesn't know to have the idle valve lock it down to idle.

Steve, thanks for responding. I hear an audible "click" when I slightly lift the idle stop and let it back down so I assume it is working. I will have to look up the readings in the Bentley manual to be sure that it is indeed operating properly. On the other hand, it was working fine prior to the rebuld.

[Rot 911]

Any of the day shift have any other ideas?

[ChrisBennet]

Do you suppose the idle stabilizer valve could be sticking open?
-Chris

[Rot 911]

Originally posted by ChrisBennet
Do you suppose the idle stabilizer valve could be sticking open?
-Chris

Well after reading another thread and going out to the car this morning and testing the theory, I think the new clutch cable I put in may be rubbing on the accelerator linkage. I start the car in neutral it is revving up to 2000 rpms, but a few pumps on the clutch and it drops back down to 850 rpms. Have to get in there and look tonight. I will also check the idle stabilizer valve to make sure it is operating properly.

[ChrisBennet]

I've had accelerator linkage hang up on the clutch cable right near the transmission bell crank. When you tighen the nuts (15mm wrench) on the clutch cable, it should lie right up against the side of the transmission.
-Chris

[Rot 911]

Originally posted by ChrisBennet
I've had accelerator linkage hang up on the clutch cable right near the transmission bell crank. When you tighen the nuts (15mm wrench) on the clutch cable, it should lie right up against the side of the transmission.
-Chris

Thanks for the additional suggestion! I would much rather it be a mechanical problem then an electrical! Much easier to diagnose and fix.

[dhoward]

Originally posted by Kurt V
I checked and the linkage is not binding or hanging up. In fact the idle would jump up to 2000 rpms even with the linkage disconnected....

That would probably discount the clutch theory. Man, if you had carbs, I'd have a few things for you to check....

[KTL]

Can't hurt to adjust the idle and clean the ISV.

Take off the ISV and shoot some electrical parts cleaner in there. That should dump out some dirty solvent. Reinstall and adjust idle.

Get car to operating temp. Then go over to the fuse panel socket on the right side of the panel. Jumper the pins at 1 o'clock and 6 o'clock with a homemade piece of wire and pin terminals, or use a round relay. I think John Walker said a red relay is the right one to bridge the two aforementioned pins. edit: It's a black relay that works. You pop the top off and push down on the contact with your finger to bridge/activate the jumpering- thanks to John Walker. Can't remember for sure though. Anyway, jumpering the socket is what disables the ISV.

Adjust idle to factory rpm spec. with pins jumpered. Remove jumper and check idle. JW recommends to continue this procedure of jumper, adjust, remove jumper, check idle/adjust, jumper again........... until the idle does not change when jumpered or not.

[THECARREAPER]

my next step... grrr new ICV did not fix hunting idle when warm. grrrrr.

[rusnak]

Check all of the ground points. The ECU may be going into limp mode.

The Bentley manual has an excellent troubleshooting section. Check the obvious stuff first before whipping out the digital multimeter, then go through the Bentley manual.

[cliyde]

Same here, check to see if the cable is resting on the linkage.

Originally posted by ChrisBennet
I've had accelerator linkage hang up on the clutch cable right near the transmission bell crank. When you tighen the nuts (15mm wrench) on the clutch cable, it should lie right up against the side of the transmission.
-Chris