740 GL Idles up and down

mattp · Post by **mattp** » 28 Nov 2002, 18:16

In the morning when I start my 740 it idles really high then all at once the idle drops to about 300 RPM and the check engine light comes on. The idle normally goes back up to about 900-1000 but then it drops again...It just keeps going up and down...up and down. Also once I get going the car seem to speed up and slow down by itself!?!?!?! MAJOR SAFETY HAZARD. And at Red lights it idles about 5-600 rpm and gets REALLY rough...the car vibrates and acts like it wants to stall...ANY IDEAS?? I put a new cap and rotor on....and a new fuel filter HELP PLEASE!

elerner1 · Post by **elerner1** » 02 Dec 2002, 01:45

I believe you have a problem with the constant idle system. There is a motor that adjust air flow to the intake manifold to keep the idla at a constant speed. Your is cycling up and down. It is controled by a computer. Expensive to repair. Good luck.

elerner1 · Post by **elerner1** » 04 Dec 2002, 17:53

Just curious about an update on your problem. Ed

mattp · Post by **mattp** » 04 Dec 2002, 20:43

Have an appt. mon. at the dealer....they are thinking maybe a throttle positioner..

BONG(240 2FAST 4 U) · Post by **BONG(240 2FAST 4 U)** » 10 Dec 2002, 23:30

ALOHA,I HAVE THE SOLUTION FOR YOU.JUST REMOVE THE T-BODY,
CLEAN THE T-BODY WITH CARB CLEANER,THEN LOOSEN THE TP SENSOR,
THEN THE 8MM NUT ON THE ADJUSTMENT,THEN TURN THE SCREW IN UNTIL THE PLATE GOES HALF WAY ON THE SMALL HOLE,NOT THE BIG ONE,THEN ADJUST THE TP SENSOR SO WHEN YOU OPEN THE THROTTLE
IT CLICKS,THEN REINSTALL THE T-BODY WITH A NEW GASKET.
******AFTER THAT IS ALL DONE,TURN THE KEY ON AND ON YOUR
DIAGNOSTIC CONNECTER ,PUT THE WIRE INTO EITHER THE #2 OR #6,THEN PRESS IT THEE TIMES,THEN YOU WILL HEAR THE INJECTERS CYCLE,THEN THE IAC MOTOR WILL CLICK,WHEN IT CLICKS,SPRAY SOME
CARB CLEANER INTO THE IAC HOSE ON THE INTAKE HOSE,THIS WILL
CLEAN THE IAC MOTOR AND IT WILL RESTORE YOUR CAR IDLE AND IT WILL BE MORE RESPONSIVE.

BubbaHo · Post by **BubbaHo** » 04 Mar 2004, 16:53

mattp wrote:Have an appt. mon. at the dealer....they are thinking maybe a throttle positioner..

Having a very similar problem with our 1985. Did you find the problem with the uneven idle problem.

Volvord · Post by **Volvord** » 05 Mar 2004, 16:05

Two items that could cure this problem:

1) clean the throttle body, the interior of the TB will get coated with fuel deposites and effect performance, the best method is to remove the thottle body and clean it using some spray carburetor cleaner. Then reinstall using a new gasket. Set the throttle position sensor with the engine off, loosen the set-screw and adjust the sensor so that it "clicks" when the throttle shaft is moved slightly.

2) remove and clean the Idle Air Control motor with the same carburetor or throttle body cleaner. The deposites will also effect the performance of the IAC motor and cause the idle to hunt, cleaning usually cures the problem.

J-Roc · Post by **J-Roc** » 27 Apr 2004, 00:29

Hello Volvord,
Where's the IAC located? I'm working on a friends '91 740 4cyl and the idle hunts up and down approx.300 rpms in Park and in Drive at a stop. The idle gets low at times and begins to shake the whole car as if it hadn't any motor mounts.

Does anyone have any links or instructions on how to pull codes manually? Do you have a guide that shows what each code means? Thank you for any info!

-Jeremy

Volvord · Post by **Volvord** » 27 Apr 2004, 19:41

It is a small motor (metal cylinder) with air line connected to it located under the intake manifold.

A.Baker · Post by **A.Baker** » 30 Apr 2004, 09:44

"STOP" Do not go to the dealership. (yet) Do this test first. Remove the idle control motor. Plug off the black rubber hoses. Start engin and watch the motor. It will have a guillotine typ valve in side. it will open and close as the RPM range changes. If this happens your motor is good. If you need a motor DO NOT get one form the dealership they are 250.00$ or more. E-Mail me your part # and if they match I will send you a good one for 0$ other wise hit the bone yards I got one for 25.00 As for the TPS it only lets the ECU know when the throtle is off idle. Next there is a sensor below the intake between the #3 and #4 cylender. it tells the ECM what tem the engine is and the ECM controles the Idle speed motor. I have a 740 that had the same bad habit as yours dose.Test the sensor w/an Ohm meter. An open circut will cause this condition. Do not forget the copper washer when you replace the sensor. One more thing Disconect the neg. battery cable. Pull the conector off of the ECM under the R/side kick panel and look @ all the pins. Clean/replace the bad ones. Hope this helps.
Let me know if this helped. If you need a schamitic I think I can E-Mail you one

Good luck