1998 STS stalling at idle

[aguthmiller]

I have a 1998 Seville STS thats been stalling at idle. At first it only did it when the engine was cold about 2-3k mile ago. Now it's stalling all the time on idle. It's got about 114K on it. New plugs, wires, pcv, & tb cleaning at 100k. It seemed like it was idling rough, even before it started stalling. Replaced FPR about two months ago. Took it to the local GM dealer who couldn't get it to stall. They checked "ignition system, egr, & fuel pressure". I made them pull the misfire counts. They reported "#4 @ 480, #8 @ 0, & the rest 200-300". They said that wasn't "that high". I replaced the IAC valve earlier tonight. It actually seems to be idling a lot smoother now, but stalls now after about 15 seconds of idling after driving for 5 mins. It has never stalled during deceleration. No codes except P1599 (stall detected).
It starts right back up, but will immediately restal if it don't put pressure on the pedal within a second of it starting. If let go of the pedal after bringing the rpm up, it will idle ok for 15-60 seconds (sometimes longer before replacing the IAC), then just die.
Any ideas??? CKP, even though it's never stalled during decel and it's pre 2000?

[Ranger]

Clean the TB.

[aguthmiller]

Originally Posted by Ranger

Clean the TB.

As I said, I did that at 100k when I bought it. It was actually fairly clean in comparison from others I've done. It might've had something to do with the fact that when I bought I drove it from New Jersey to home in Minnesota in less than 24 hours. I'm also fairly heavy footed. The car sees 100MPH on a back road once a week and it passes 5K RPM getting there.

You think it would still have build-up? I can clean it again if you think so.

[Ranger]

Nah, once a year is good. So is WOT. Sorry, I missed that you did that already. Failed CKP sensors on pre 2000's are not common. Is the battery OK? It will die if the voltage gets too low. Might want to check your fuel pressure since we do not know if it is fuel, ignition or air starvation. You might have a weak or intermittent fuel pump.

[aguthmiller]

Originally Posted by Ranger

Might want to check your fuel pressure since we do not know if it is fuel, ignition or air starvation. You might have a weak or intermittent fuel pump.

I've checked the fuel pressure and so did the dealer, but if it's intermittent... I should try to get the guage on it when it having proplems.

Originally Posted by Ranger

Is the battery OK? It will die if the voltage gets too low.

I've never thought about that. It always cranks ok and starts back up. Dash lights seem bright. I'll watch the volt readout while its idling. I have noticed that when I was opening the doors in the fall (and the accessory power would come on) the radar detector would go crazy like the voltage was low, but the car always started fine.

[Ranger]

Maybe corrosion on the cables?

I once had a Chevy Blazer with an intermittent pump that would fail and always restart.

[aguthmiller]

Originally Posted by aguthmiller

I've never thought about that. It always cranks ok and starts back up. Dash lights seem bright. I'll watch the volt readout while its idling. I have noticed that when I was opening the doors in the fall (and the accessory power would come on) the radar detector would go crazy like the voltage was low, but the car always started fine.

Originally Posted by Ranger

Maybe corrosion on the cables?
I once had a Chevy Blazer with an intermittent pump that would fail and always restart.

Voltage on DIC stays steady at 14.5 or so right before and during the stall. 12.1 volts after stall. No corrosion on the battery under the back seat. Cables are tight.

Originally Posted by aguthmiller

I've checked the fuel pressure and so did the dealer, but if it's intermittent... I should try to get the guage on it when it having proplems.

Got to see the fuel pressure during a stall tonight... 47 PSI while idling. Slight dip to 45 then a split second jump to 50 psi during the stall (it only takes a second, it stalls like you switched it off). Settles at 45 PSI.

Since my last post, I've replaced the TPS and the PVC. I cleaned the EGR valve and replaced the gasket tonight. The cars idles silky smooth now, right up until it stalls in an instant.

Also now the car will stall during coming to a stop (before I'm actually stopped). I've had it stall pulling into parking spaces. Tonight it stalled when comming to a stop fairly quickly from 50 MPH just before I actually stopped.

Any ideas???? help!

[aguthmiller]

Almost forgot, pulled a current P0741 from it tonight. Could the TC be getting stuck engaged or engaging while stopped and causing the stall even in Neutral? Or completely unrealated? I'd think I'd feel a jerk or have seen the engine jump.

[Ranger]

Sounds like you have ruled out the fuel pump. Pressures look good.

P0741 is TCC stuck off and that will not cause a stall. P0742 is TCC stuck on and will cause a stall.

Maybe it the CKP sensors. They do not always throw a code. That said, the '98's where not known for bad ones, but you are running out of possibilities.

[aguthmiller]

Replaced CKPs and CMP last Saturday (8 days ago). It's been running good since! Thanks for the help, Ranger. I replaced the CMP basically because I was putting in the order from Rock Auto and for a $28 part it wasn't worth chancing it being the problem and having to pay shipping later. These sensors where pretty much the only ones that could cause the problem that I hadn't replaced, after all.

The CMP took all of 5 minutes to replace. The CKPs took about an hour to hour and a half. It's not difficult, just a little tight and very oily. The top oil adapter bolt is really the only problem. Certainly worth it to save the $150 in labor. Thanks to the forum for providing instructions.

[mgturbo1]

Cmp?

[Ranger]

Cam Position sensor

[mgturbo1]

Thanks