1998 Riviera stalls at low speeds (highway speeds no issues)

[katherine15]

Hi all,
I've run into another issue with my 98 supercharged riviera. At low speeds, usually anything under 50 km/h the engine stalls and loses power. The battery and oil pressure light come on, but it starts right back up and goes away. No check engine light comes on either, so I realize this may be tricky to diagnose.
The frustrating part is that it doesn't always stall out, so I can't exactly show my mechanic and have him drive around to experience it. It happens sometimes, and sometimes it doesn't. Enough to leave me scratching my head...
Anyone have similar issue? For reference, I have had the coil pack replaced, new spark plugs, new wiring, new O2 sensor, and new fuel injectors. All I can think of is it may need new fuel pump...?
Appointment with my mechanic is booked, just looking for more insight. Hoping this sort of repair isn't going to break the bank.
Thanks!

 

[MelsRegal]

Check with your mechanic if the SC 3.8 uses an idle air control valve, looking at parts sites it is unclear. It would be located on the throttle body. Might be worth a glance to check if the throttle body needs a cleaning.
I assume it never stalls when you come to a stop?

 

[katherine15]

No it never stalls when I come to a stop. I will mention this all to mechanic.Thanks

Check with your mechanic if the SC 3.8 uses an idle air control valve, looking at parts sites it is unclear. It would be located on the throttle body. Might be worth a glance to check if the throttle body needs a cleaning.
I assume it never stalls when you come to a stop?

 

[katherine15]

Update, it stalls almost every time I come to a stop. Taking it to my mechanic ASAP. What else could it be?

No it never stalls when I come to a stop. I will mention this all to mechanic.Thanks

 

[katherine15]

Full update,
Took car to my mechanic, he checked for codes and there were none. Car also didnt stall out at all on him either, so he was left scratching his head. I explained all the instances that it had lost power and unfortunately couldn't recreate it. Anyhow, he cleaned the MAF sensor and said that debris or dirt could make it malfunction.
So far so good, I drove around at highway speeds, slower speeds, and even idled and drove around parking lot. No loss of power.
Hope this was the fix I needed....
I asked about throttle body cleaning too and he did that as well.
Fingers crossed I can make it across canada in my riv in a couple weeks

Check with your mechanic if the SC 3.8 uses an idle air control valve, looking at parts sites it is unclear. It would be located on the throttle body. Might be worth a glance to check if the throttle body needs a cleaning.
I assume it never stalls when you come to a stop?

,

 

[LARRY70GS]

Crank sensor can do that as well. I would not replace the fuel pump, I would monitor fuel pressure and see what it does when stalling. Usually fuel problems manifest as a slow stall, not instant like ignition. A crank sensor will not light the CEL.

 

[katherine15]

Hmm I will mention that to my mechanic. I'm just surprised that based on all the info I'm providing; I'm getting the best answers from Google, rather than a registered mechanic who works on cars all day long. (No offense but you only know what I'm reporting, not what the car is actually doing.)on the drive home it stalled and lost power 4 times in 4 km. All at about 50-70 km per hour. To set scene, it's about 10 degrees Celsius, engine is running fairly cold, the rpms are normal, about 1.5 to 2.5, and all of a sudden it stalls out, sometimes it jerks, other times it's as if I just ran out of gas. Usually it starts right up with no hesitation, but tonight it was sputtering and struggling to get powered back up atleast once. As far as I'm concerned it is unsafe to drive....obviously I dont fully understand what crank shaft sensor is or what it does, could you please explain to me so I can have an intelligent conversation with my mechanic and ask him to replace it?
Thanks. I'm stumped and need to figure this out. I would be so lost without this forum and its active members. QUOTE="LARRY70GS, post: 359860, member: 726"]
Crank sensor can do that as well. I would not replace the fuel pump, I would monitor fuel pressure and see what it does when stalling. Usually fuel problems manifest as a slow stall, not instant like ignition. A crank sensor will not light the CEL.
[/QUOTE]

 

[HotZ28]

I once had an inferior new MAF that was installed & caused the same problem with stalling. I replaced it with a Hitachi unit and have never had another stall problem since while driving. Have you, or the mechanic checked fuel pressure? Have you tried disconnecting the MAF to see if the stalling continues? You could have other problems, but I just wanted to share my experience with an Series II S/C engine. Good luck and I hope you find the solution soon.

 

[LARRY70GS]

The crank sensor requires that the harmonic balancer be removed. Then it's a simple bolt on bolt off. You'll need a balancer puller to get it off.

The MAF can be checked with a scan tool. The MAF tells the computer how much air is entering the engine, and the computer uses that information along with other sensors to determine fuel injector pulse. If the MAF is causing the stalling, you will see that on the scan tool. The reading are in grams/hour or grams/minute. The reading will be excessive causing the engine to run very rich, and the fuel trim numbers on the scan tool will be very negative (>-15%). That indicates the computer is trying to pull fuel out because of the rich condition. You can see this on a good scan tool.

 

[Amanda Hugenkiss]

Old thread but chiming in. Anything OBD2 there is no excuse for a "mechanic" to be guessing and throwing parts at problems. He should hook up his scan tool and read live data from various inputs and see what is happening. As a DIY I may make an educated guess and try swapping a part but for a paid mechanic that's not acceptable. With today's scan tools even a DIY can see what is going on with the sensors. The complete incompetence and cost of professionals is what drove me to learn to do everything by myself.