1998 Tahoe Randomly Stalling

[BCM08]

Our Tahoe is having a stalling problem. It is most common when slowing down to come to a stop, and sometimes when I start goin again it will hesitate hardcore and sometimes jerk. There is no SES light. I checked under the hood, all connections are good, air filter is new, spark plugs have ~20k miles on them, fuel injector cleaner was recently ran through, fuel filter is new. It's done this before but after letting it sit for a few minutes it was fine.
The truck has 124,6xx miles on it. When in park it will idle/rev perfectly fine.

 

[shreksbrother]

Speaking from experience of my '98 (yours may have a completely different problem)... I noticed a similar situation with mine. Once I noticed no check engine light, I figured it had to be downstream of the motor, either tranny or exhaust. I had my cats cut off and one of them was hollow. I now am going to replace my muffler, as I'm guessing the stuff from the cat clogged it up. Of course until I fix it it's just a theory, but I did disconnect my exhaust between the cats and muffler, and it idled (in gear) just fine.
Something to check, anyhow. If you have one of those infra-red thermometers, perhaps you could run the truck for a while and start checking the temp along the exhaust afterwards. My theory is it would be significantly hotter downstream instead of cooling.

 

[95TwinTT]

Our Tahoe is having a stalling problem. It is most common when slowing down to come to a stop, and sometimes when I start goin again it will hesitate hardcore and sometimes jerk. There is no SES light. I checked under the hood, all connections are good, air filter is new, spark plugs have ~20k miles on them, fuel injector cleaner was recently ran through, fuel filter is new. It's done this before but after letting it sit for a few minutes it was fine.
The truck has 124,6xx miles on it. When in park it will idle/rev perfectly fine.

Could you elaborate a bit on conditions? Like when slowing down, does it jerk at a certain speed, or just as it comes to a stop? What happens to the rpm's? Does it make any difference if the engine is warmed up or not?

Any mechanical noises associated with it? Ever hear any backfiring? Are all the sensors original as far as you know like MAP, TPS, MAF, O2?

You mentioned it has happened before. When did it stop and when did it start again?

 

[tahoeman21]

hesitation....

I had a similar problem with my 99 tahoe..... my hoe would accelerate poorly from a complete stop... it would hesitate like if the engine wasn't getting enough gas. So finally the SES light came on.... took it to my mechanic... he scanned the computer, and the MAF code pops up, it said that it was 'Out of Range' meaning that my MAF was messed up..... most of the time the SES did not come on either.... so my mechanic replaced the MAF, and problem solved.... i went with a remanufactured MAF to save a few bucks...

 

[BCM08]

Could you elaborate a bit on conditions? Like when slowing down, does it jerk at a certain speed, or just as it comes to a stop? What happens to the rpm's? Does it make any difference if the engine is warmed up or not?

Any mechanical noises associated with it? Ever hear any backfiring? Are all the sensors original as far as you know like MAP, TPS, MAF, O2?

You mentioned it has happened before. When did it stop and when did it start again?

It dies when slowing down when I get to around 10-15mph. The few times it has jerked when accelerating when I drove it was ~10mph. The rpm's drop as the normally do when slowing down and when I get to around 10-15mph the tach just drops to 0. Only happens when the engine is warmed up.

There aren't any mechanical noises or backfiring. It basically acts as if I turn the key off. All sensors are original.

The last time it happened was almost a year ago, and it only occured one time, and after letting it sit for around 10 minutes it was fine. Now it happens every time it is driven.

The transmission was rebuilt 2,000ish miles ago, but I don't know if that would have anything to do with it, last time it happened was before the trans. rebuild.

 

[95TwinTT]

I think Tahoeman21 has narrowed it down here. If this is fairly consistant problem now, I would find someone with a good code reader and go for a test drive. There are code readers that do more than just decode the SES code. They can actually dial up various sensors and read their output, while driving. You can monitor the MAF filter readings when the truck is acting up and quickly determine if that is the problem.

The SES codes are great for pointing out a lot of problems, but they can't possibly program for every single thing that can go wrong.

The problem not happening when the engine is cold, is also important.

 

[BCM08]

I took a vid of exactly what it does tonight.

 

[95TwinTT]

Is there a chance that the transmission is involved. It sounded like there was a clunking noise It's a long shot, but I wonder about the locking torque converter. Just to humor me, try slipping it into neutral just as it starts to happen. See if that keeps the engine from killing.

 

[BCM08]

Could be a possibility I guess. The transmission was rebuilt ~2,000 miles ago.

Could the EGR cause a problem like this? Sticking open causing the motor to stall when slowing down?
Or maybe something with the IAC?

 

[95TwinTT]

The EGR valve is certainly a candidate. There are a variety of things going on, while slowing down.

With it being somewhat predictable, now, I would not think something sticking would be that repeatable.

It could be the computer acting on false information from a defective sensor.

The thought about the locking torque converter a long shot, but I ran across a car that had a similar problem, years ago. If you had a complete trans rebuild a few thousand miles ago, typically the entire torque converter is swapped out for a rebuilt one. I think you mentioned that this problem happened before and after that rebuild, so that would eliminate the mechanical part of it. If they just freshened up the clutches and replaced the filters, they could have left the same TC on there if the fluid looked clean.

It will probably come down to going for a test drive with a monitor hooked up to your ECM. That could quickly eliminate some of these questions.

Or you could try unplugging some of the items, one at a time and test. Like the MAF sensor. Then the Idle Control Motor. Then I would try even O2 sensors.

It has to be frustrating to say the least. Keep us posted..............

 

[blk87brd]

I had the same problem with a faulty EGR Valve. Changed it and problem solved. I hate fixing things by changing components until the problem goes away, but EGR would be my first guess.

 

[95TwinTT]

I agree, firing the parts cannon at these things can quickly get expensive.

Maybe you could pull one of the hoses off the EGR valve just to see if you can change the symptoms.

Oops! / Edit...........................>>>>>

I just glanced at the schematic. It appears that your truck has a totally electric EGR Valve. It should have a five condutor plug. So don't look for hoses, just one plug should unhook it.

 

[tahoeman21]

BCM08.... i feel you on this one.... it sucks, to me it looks like a fuel/electrical issue... have you replaced the fuel regulator recently? if you haven't there's a good chance that the engine's fuel rail is not getting the right fuel pressure, causing the engine to die, therefore, the regulator became weak... for the electrical part, i would start tackling the battery terminals, they may have become loose or the cabling to the alternator, may be a loose cable too.... definately not a tranny problem!! i saw that it rev fine when it was on neutral but it starting hesitating when it was under load (i mean in Drive) so i would definately start with the fuel issue.... best wishes.

 

[T-Bagg]

This sounds exactly like what my '98 is doing right now. It started with just the stereo shutting off. And evolved into the conditions you're describing. I would guess it's because your alternator isn't making a reliable charge. At least that's what it is for me. My alternator is shot. But it does sound just like the way my truck is behaving. So I'm upgrading to a high output alternator. And I figure since I got the amps. I upgrade the whole ignition system.

 

[95TwinTT]

I don't think it could be related to the alternator. If you watch the volt meter, it never drops below 14 volts while running. It also spins the starter fast, so the battery must be charging just fine.

 

[BCM08]

Somewhat of an update..

My dad ran seafoam through it a few days ago, and now when it's warmed up we can't even back out of the driveway without it stalling.

Where can I find the EGR? If I do find it, how can I tell if it's bad or not?

 

[95TwinTT]

The way it starts right back up without a problem would seem to eliminate a lot of ingition questions.

Did you try unplugging the EGR valve? Seafoam would not do a thing to loosen a sticking EGR. Do you have access to a fuel pressure guage?

The Idle Control Motor is a stepping device. I don't think those things are subject to sticking, although they are spring loaded to a degree. If unplugging the EGR does nothing for the problem, try unplugging the idle control motor. That would at least eliminate them from the list.

Has the problem ever changed by filling the fuel tank. I noticed in your video, it was at a quarter of a tank.

 

[BCM08]

The way it starts right back up without a problem would seem to eliminate a lot of ingition questions.

Did you try unplugging the EGR valve? Seafoam would not do a thing to loosen a sticking EGR. Do you have access to a fuel pressure guage?

The Idle Control Motor is a stepping device. I don't think those things are subject to sticking, although they are spring loaded to a degree. If unplugging the EGR does nothing for the problem, try unplugging the idle control motor. That would at least eliminate them from the list.

Has the problem ever changed by filling the fuel tank. I noticed in your video, it was at a quarter of a tank.

I don't know where the EGR is so I haven't been able to try that. I don't have access to a fuel pressure gauge, I wish I did.

Where is the idle control motor?

I think I remember my brother saying something about that it was fine until it got under 1/2 of a tank. I'm not really sure how that would effect it though.

btw I appreciate all the help and suggestions.

 

[95TwinTT]

I'm a little fuzzy on the layout of the 98 model, but the EGR should be right behind the throttle body on the passenger side of the intake manifold. The electrical connector will have five wires going into it.

The Idle Air Control has more of a square plug with four wires going in. I am guessing but I would look for it on the side of the throttle body, towards the rear on the passenger side.

Maybe your truck is new enough to have the plastic fuel rails, I don't know. I don't look at stock engines very often. lol

 

[Whippled2dr]

The EGR on the 96-00 vortecs are on the front of the intake manifold, right next to the thermostat housing.