Jakerx

Hey guys

After adjusting my idle, my idle is normal at cold start and normal most of the time. But after say 20 minutes of driving, it'll jump up to 2000 rpm and stay around there. I disabled the idle stabilizer valve as per instructions before adjusting idle, and waited for the car to warm up. Any ideas on the problem?

Danno

Bad stabilizer? Or a big vacuum leak somewhere?

Jakerx

doesn't the idle stabilizer valve only work to a certain point until the engine is all warmed up and good to go? i don't think it would be a vacuum leak...all the hosing was replaced a short while ago...

Charlotte944

When the throttle plate closes the TPS Idle switch closes (This switch makes a soft click as the throttle opens and closes.), sending a ground signal to the DME. When the DME sees this ground it "knows" the throttle is closed and the engine should be at an idle. The DME checks engine RPM, and based on that input either opens or closes the ISV to bring the engine to idle.

If the engine RPM is too high (like in an Over Run, or Trailing Throttle condition) the DME shuts the injectors off until engine RPM drops below the Over Run setpoint where the DME shifts to using the ISV to control engine idle RPM.

If either the TPS or the throttle body are not adjusted properly you can get in a situation where the engine will "hunt" trying to find idle. This is caused by the DME seeing an Over Run, shutting off the injectors, RPM drops, injectors fire, RPM rises, and so on.

If the ISV is functional, but the engine RPM rises above a normal idle, then I would suspect either a faulty/misadjusted TPS, an intermittent open in the TPS connector/cable, a misadjusted/sticking throttle cable, or a sticking throttle.

In light of that I would start by removing the throttle body and verifying that the TPS is functional, and that the throttle plate will close.

Once you have verified the TPS and throttle body are OK, reinstall the TB, connect a dwell/tach to the coil, install a jumper between pins 'B' and 'C' at the diagnostics connector and start the engine. Using the idle by-pass on the TM, set the idle to 840 +- 50 RPM. Blip the throttle a couple of times to verify the engine returns to idle. Remove the jumper from the diagnostics connector. Engine idle may change slightly, but should stay within +- 50 RPM. Turn on the A/C, headlights, and fog lights to load the electrical system (and consequently the engine). If the ISV is working properly the engine should stay at a normal idle.

Jakerx

thanks...i'll be getting to that this weekend...

tod84944

Jake,
Did you adjust the idle with the set screw for the stop on the throttle cam? If so, you probley turned it just enough to by-pass the contact points on the switch, and as Charlotte said, the dme thinks that the throttle is open.

tod84944

Oh ya, heading to Greyhound here in a few to drop off the box. You will be 951 looking in no time!!!

Jakerx

haha SWEET! i can't wait to get it! but i will also be completing a few interesting things to the car that will make my car more "951 like" within the next couple weeks *hint hint*

but back to the problem...yes i did adjust idle with the set screw for the stop on the throttle cam in place...although i did make sure that it still clicks properly...is the clicking not enough? do i need to go in and redo it you think?

tod84944

I would start by turning it back a half turn.

Jakerx

when you say half turn you mean the throttle stop and not the idle screw am i correct?

hosrom_951

Fully close the throttle screw (do this when the engine is warm, running and already bypassed the ISV), then turn it ~1/2 turn clockwise (if i remember). Should be sitting between 900rpms.......

Charlotte944

Yep!

What you need to do is pull the TB, loosen the TPS screws, and back out the mechanical stop screw until it is not touching the mechanical stop arm. make sure the throttle plate is fully closed, and turn the stop screw in until it just touches the stop arm, turn it in another 1/2 turn, and then lock it down with the jam nut.

Now you can set the TPS so it clicks just as the throttle plate starts to open.

Reinstall the TB and you're ready to set the idle.

HINT: When you connect the throttle cable make sure the TPS still clicks!

Jakerx

problem solved...bad idle stabilizer valve...when it was at 2000 or so i disabled the idle stabilizer valve and voila everything was perfect. i've left the wire in there. 7 hours later i started the car up for a cold start and had no problems with idle. haven't some people deleted the ISV before?

Charlotte944

You could remove the ISV and block off the plumbing.

However, cold starts may be problematic, and the idle may drop under load (A/C on for instance), which is why the ISV is there in the first place.

Jakerx

i have not had any problems with cold start so far. as for a/c...i haven't had it charged yet. so i guess we'll see how it is when i do the recharge...thanks for all the help clif