stalling at low idle only 1991, 740 GL 164,000

Ron Richison · Post by **Ron Richison** » 08 Apr 2008, 18:53

Car starts, (rough sometimes when cold) then warms up, drives ok for 4-5 minutes. At full speed, car runs GREAT. Responsive, no hesitations or misfires of any kind. When the car comes to a stop, at idle, it feels and sounds like it's "missing" and will eventually stall. I have replaced plugs, wires, cleaned throttle body, replaced flame trap, air idle control valve and mass air sensor. I'm running out of MONEY!
Thanks for any insight from anyone that can.

Ron

Post by **jonesg** » 09 Apr 2008, 17:49

Did you check the TPS on the throttle body, it should click as throttle starts to open and just as it closes fully,

that turns on the idle control motor.

Did you try the faq files?
http://www.brickboard.com/FAQ/700-900/E ... mptoms.htm

Ron Richison · Post by **Ron Richison** » 09 Apr 2008, 18:30

should you hear the click even without the car running? I tried this before and heard an audible click, but the car was not running. I have also sprayed carb cleaner around intake and throttle body gaskets, no reaction.
also just checked codes, none present.
someone told me to pull the vacuum line at the end of the fuel rail to check for presence of fuel. I'm not sure what line that is, (there were 2) so I pulled one and found no fuel present. The other line was on there so tight I didn't want to take it off, so I didn't.
the previous owner suggested O2 sensor, but to be that would only kick in after car is hot. ??
How likely would it be for the entire ECM to go bad??

Thanks, Boston, you are my only response!

Post by **jonesg** » 09 Apr 2008, 19:42

I suspect a bad computer would cause fault codes, bad connections at the computer plug are common though.

Pull the vac line from the fuel pressure regulator, its at the front end of the fuel rail, there should be no gas present.

The click is a physical switch, you can hear it when engine is not running.

when its running rough find out why and where,

pull spark plug wires to find a bad wire or sparkplug,
try unplugging fuel injector plugs til you find the bad one, check for healthy spark at all plugs (when its running rough).

read the faq, see if you can match your symptoms,
http://www.brickboard.com/FAQ/700-900/E ... mptoms.htm

Ron Richison · Post by **Ron Richison** » 09 Apr 2008, 21:33

I checked out the link, very helpful. thanks.
some very similar symptoms had these fixes: fuel pump relay; tps; but the overall winner was fuel pressure regulator. I pulled the vacuum line and found no gas present, I disconnected the return line and it was pumping plenty of gas (into a gas can, of course) so, that tells me it's ok. one other fix was a "hall sensor" (never heard of it).
Thanks for the link.
When I unplug each injector, what should I be listening for??
Thanks Boston, I'm not giving up

Post by **jonesg** » 09 Apr 2008, 22:07

On a 1991 you do not have the hall sensor, they got away from that methinks in 89.

check the sensor on top of the tranny bellhouse, look down past the distributor with a flashlight, run your hand down the wire, the insulation goes south and falls apart right near the sensor. Its the TPS , throttle position sensor or something like that.

fuel and electrical problems mimic identical running problems and its difficult to diagnose , its actually easier if the car will not run.

A bad fuel pump can feel like hard shifting of gears in an auto, mine was lugging as if it was in the wrong gear but it was the fuel pump, go figga.

Ron Richison · Post by **Ron Richison** » 11 Apr 2008, 21:55

I checked out all the sensors I could find. unplugged and replugged, all looked fine. I even pulled the O2 sensor, it looked fine. I replaced the fuel pressure regulator (a suggestion from another site) still no fix. The only thing I haven't done yet is a new fuel pump relay.
again, here's my problem, maybe there's something else that I'm not thinking of.
Car runs fine at speed but acts erratic at stop. Idle is rough and will die eventually. When in park or nuetral it's better than in gear, but still roughs a little rough.
recap on what I've done: new air mass, new idle air control, new fuel pressure regulator, new flame trap, checked all vacuum lines, plugs and wires.
What can I rule out because it runs so well on the road? why the problem only at a stop?

Post by **billofdurham** » 12 Apr 2008, 11:52

Have you checked the coolant temperature sensor and its connections?

Have you checked for fault codes?

Bill.

Ron Richison · Post by **Ron Richison** » 12 Apr 2008, 14:36

so far no codes.
i've checked all the sensors for good wiring and conections.
someone suggested filling my tank, previously it was about 1/4. No immediate reaction, but seemed much better after about 10 min. Does this tell me something about the fuel pump and or sysytem?

Post by **jonesg** » 12 Apr 2008, 16:15

I don't think its the fuel pump.
Sounds like something in the idle circuit, idle speed motor , or...

you say you looked at the sensors , the engine coolant sensor which signals the computer isn't something you can just pull out without a bit of work, I had to pull my intake manifoold back just to be able to see it.

Theres 2 coolant sensors on the same side of the block, the front one you can see, but the one that sends a signal to the computer for the start up fuel/air mix is at the back of the block, under the 3rd cylinder intake manifold. It can be tested but if I were going to the trouble of looking at it I'd just install a new one because the intake manifold gasket is going to cost $10 anyway so why re-install used parts.

But its odd you're not getting any codes, that could very well be an intake side air leak, vac lines, intake manifold gasket, throttle body gasket, intake bellows tube, these are all big trouble areas.

Its a pain in the butt to try track it down, I find ether , used carefully, can pinpoint air leaks better than propane.

The time to track it down is when its running like crap.

And I wouldn't completely rule out the fuel pump as yet, my bad pump ran fine at speed but low end acceleration was real bad.