Stalling 99 STS mystery

whack_lac · #1 (**permalink**) 03-16-07, 10:54 AM

Hello, I have a 99 STS with 92K. Ocassionally when I am stopped or almost stopped the car will stall out. It always starts right back up. I have replaced both crank sensors, plugs & wires, new EGR valve, cleaned the throttle body, and run a can of TEC through it. The car has always run very well aside from the stalling up untill recently when I noticed that especially when the engine is cold it will 'shudder' at about 1100rpm. It runs smooth at any other rpm, but when I hold it at 1100 it almost seems as though its missing.

Heres a funny thing, after changing the plugs and wires and cleaning the throttle body yesterday, it began stalling at almost every stop. Where as before it was a once every couple week issue. I am assuming something I touched when changing plugs/cleaning throttle body is the culprit.

After stalling yesterday I didn't have any codes except the 'engine stall or near stall detected'.

In the past I have pulled the following codes;

U1064 - Loss of Communications with DIM - this one I get pretty often

and one time I got either

U1056 - Loss of Communications with RSS
or
U1066 - Loss of Communications with RIM
I can't remember which, but it was a while ago and it has not returned.

I did remove the coil pack when changing plugs and when I cleaned the throttle body I had to unplug a couple sensors, but other than that I didn't fiddle with anything else, unless maybe I leaned on something. I am at my wits end. Please, I pray to the Cadillac God, please send me a fix!!!

Mountie · #2 (**permalink**) 03-16-07, 11:59 AM

All's I know is I had a simular problem ( not quite as bad)....

Vacuum leak? I found on top of my throttle body, a leak due to cracked rubber fittings. One way to search for a leak is when at idle, spray a carb cleaner around fittings to cause a stumble, helping to locate a leak.

whack_lac · #3 (**permalink**) 03-16-07, 12:30 PM

Thanks, I'll look into that. Unfortunately the car won't even idle anymore!

I'll do a visual inspection and check back. I was tugging on the vacuum lines a little.

The car will idle now that the engine has cooled off. I'm a little hesitant to spray carb cleaner around under the hood (won't it eat away at wire coatings and such?) I visually checked for vacuum leaks and found nothing. If there is one it's very small and I don't imagine it would be the culprit.

Earlier today when I drove the car it would stall every time I came to a stop, and would not idle when the engine was warm.

Mountie · #4 (**permalink**) 03-16-07, 01:34 PM

If your inj. is set up as mine is, the crack was on the top of the throttle body opening area. There is a rubber fitting recieving 3 vacuum lines & plugs into the top, with a plastic 'snap' to hold it on....... the plastic snap holder was hiding the crack. My car would stall first thing in the morning, ( I mean, just shut off), then I would start it up again, and it was fine for most of the day, after getting up to temp..

whack_lac · #5 (**permalink**) 03-16-07, 06:22 PM

I can't find any vacuum leaks. I don't think that is the cause. The car runs fine when cold. It's when it warms up and the sensors kick in that it dies. I let it sit for 5 mins after dying to see if a code popped but nothing showed. I am at a total loss.... PLEASE HELP!!!

JimD · #6 (**permalink**) 03-16-07, 06:35 PM

Quote:

Originally Posted by whack_lac

.... I did remove the coil pack when changing plugs and when I cleaned the throttle body I had to unplug a couple sensors, but other than that I didn't fiddle with anything else, unless maybe I leaned on something. I am at my wits end. Please, I pray to the Cadillac God, please send me a fix!!!

Did you remove the ignition control module? Or did you remove all four coils individually? It could make a difference.

If you removed the entire ignition control module, are you 100% certain you installed the ground wire that fits under the module?

whack_lac · #7 (**permalink**) 03-16-07, 07:52 PM

I removed the entire module as one unit. And I did re-attach the ground. I am certain that all sensors and wires I unhooked were re-attached.

I am wondering, if I were to take the car to the dreaded stealership, their diagnostic equipment would pick up the problem as it happens(the moment of stall), correct?

**Ranger** · #8 (**permalink**) 03-16-07, 10:55 PM

Pull the IAC (Idle Air Control) valve and clean it. You may have clogged it when cleaning the TB. It is just an air bypass circuit that meters air past the closed throttle plate. It is mounted on the side of the TB. Don't confuse it with the TPS (Throttle Position Sensor) which is inline with the throttle plate axis.

whack_lac · #9 (**permalink**) 03-17-07, 04:00 PM

Thanks Ranger, I was hoping you would chime in. From reading other posts you seem to know your stuff. OK enough brown nosing. I pulled the IAC and it was pretty dirty. One question - should the plunger apparatus move freely? I pushed it in and pulled it out - which took a surprising amount of effort.

OK I cleaned the IAC and reinstalled it. I started the car and let it idle. After the engine warmed up it killed. But, whereas yesterday after it stalled and I restarted the car it would stall again almost immediately, after cleaning the IAC the car would idle for 10-30 secs before stalling again. So, possibly the IAC needs to be replaced?

Another note - when reinstalling the IAC I depresed the plunger fully so it wouldn't be in the way. When I started the car it jumped to 2k rpm and took a good 7 - 8 secs to drop down to 1k rpm. Should the valve be moving that slowly? As stated above it was extremely hard to move the plunger by hand.

I'm thinking we are on the right track here. If I give it even the slightest bit of throttle no problems at all.

**Ranger** · #10 (**permalink**) 03-17-07, 05:21 PM

To be honest, I am not sure if the plunger should move freely or not. Did you spray carb cleaner through the circuit or blow it out with air before replacing the IAC valve? Could be that it got clogged with carbon from the TB cleaning on the TB bore side.

whack_lac · #11 (**permalink**) 03-18-07, 06:34 PM

The IAC circuit is wide open, no obstructions from carbon. Back to the drawing board....

**Ranger** · #12 (**permalink**) 03-18-07, 07:45 PM

We are assuming that this is ignition related. Have you checked your fuel pressure?

whack_lac · #13 (**permalink**) 03-20-07, 03:09 PM

Ok, I purchased a Actron fuel pressure tester kit - but I can't seem to get it to work. The packaging says its for models up to 1996. The instructions say to finger tighten the fitting, but it snugs up before it makes a seal. Did they change the valve on the fuel rail after '96? Or am I just being an idiot?

**Ranger** · #14 (**permalink**) 03-20-07, 05:12 PM

It should have come with several different adapters. Maybe one of those is needed.

whack_lac · #15 (**permalink**) 03-20-07, 06:04 PM

The fitting that is attached to the hose permanently is the one for GM - there is an additional fitting for Ford(I tried this one to but it wasn't even close) The GM one fits but won't seal. If I try to tighten it any more I am afraid I will strip the plactic threads on the valve. I think I am about ready to take it to a shop and let them hook it up to their diagnostics. That or drive it into a telephone pole and say a deer ran in front of me. *sigh*