Surging and stalling at idle

92 Bravada with the vortex engine

The symptom is a tugging and surging from the engine while idling in park and stalling when in gear. The symptoms are less if I keep the RPM high and if I drop it into gear at about 2000 RPM I can get it home ok.

The problem only occurs after a full temp shutdown like when you run to the store and get back in and start it up. I can start it cold and drive it 15 miles or more with no problem but as soon as you shut it down for a few minutes or longer the problem starts again.

I checked the fuel pressure, 62+ cold and no leak down problem after 5 mins. The fuel pump and filter are less than 2 years and 20k. The engine temp is normal. Spider kit is 3 years old now. Plugs, wires, rotor and cap have maybe 15k on them.

I haven't had time to look at much yet but if anyone has an idea of where to start on this one let me know. I'm suspecting bad gas since the problem only occurs after the heat sink when you shut her down hot. I've had some real problems with vapor lock in the summer with ethanol added gas but those were a hard lock on a hot shut down, on a 100 degree day and nothing like this.

You might look at the Idle Air Control (IAC) on the left side of the throttle too.

If the IAC is OK, here are some other things to check:

No particular order other than how they popped into my head ;)

The EGR valve might have a poor seal; cleaning with throttle body cleaner or carb spray usually takes care of it.

Try wiggling the connector at the ECT, (engine coolant sensor for the ECM near the thermostat) while the engine is acting up. Push on it, pull on it, wiggle it etc. I've seen several with a loose fitting connector.

Condensation on the under side of the distributor cap can cause crossfire after a hot soak. Make sure the vent hole screens are removed inside the distributor.

Not likely, but it's possible that the ignition module heat sink compound is all crusty and not transfering the heat away from the module. The IM is very sensitive to heat. If the module gets too hot it can operate erratically. If it overheats, you won't get spark at all. Radio shack has heat sink compound in a small tube, (part #276-1372). http://www.radioshack.com/product/index.jsp?productId=2102858

Remove the module, clean off the old stuff with a rag and isopropyl rubbing alcohol, smear on the new compound and reinstall.

Those are some good ones OM.

Well thanks Chris for mentioning the most expensive part first. I pulled the IAC and cleaned the pintle head and O ring, lubricated the ring and reseated the electrical connecter. According to my repair guide you need an IAC tester to really check it out.

When Old Master mentioned condensation in the distributor cap it was like a bingo moment. The last time I drove it was before Christmas on a rainy day and I noticed a slight miss. I thought to my self then that I needed to check for condensation in the cap but after a few libations at the Christmas party and a designated driver taking me home I forgot all about it until OM's post. The girls have probably been driving it like that for months.

Sure enough, there was corrosion inside the cap, my daughters boy friend who did the last tune up had used after market parts. The cap he installed had copper spark plug wire posts instead of aluminum like the OEM, that had turned green and had corrosion build up from electrolysis. I replaced the cap and rotor with AC-Delco but, alas, the problem remains, although it does start better.

I didn't pull the EGR valve, I just sprayed carb cleaner around it with the engine running to check for leaks.

I checked the connector at the ECT, pulling it off, inspected it and re-seated it, and tried wiggling it while the problem occurs. I also watched the temp gauge while the problem was occurring and there were no fluctuations.

I'm not really sure where the Ignition Module heat sink is but I have lots of heat sink compound on hand since I'm an IT guy, just point me in the right direction.

I'm really leaning towards the idea of bad gas, between the winter blends, the ethanol and my cheap 19 yr old buying the cheapest gas it's a real possibility. The tank is a little over a quarter but I think I'll drain it off tomorrow and start with fresh gas. Thanks for the old tip on how to drain the tank Chris, just use the fuel pump. I bought a clip on tire chuck for the zert connector and have some old air hose to use. I'll use it to fill the lawn mower next spring too.

I'll keep you guys informed, but if you have any more ideas toss them out. This baby only has 246K on it now, the lowest mileage vehicle in my fleet.

Eric, Crusty heat sink compound is a long shot, but if it fixes it, it's a cheap fix. The HEI ignition module is inside the distributor on 1992 W engines, the black thing in this image:

http://i561.photobucket.com/albums/ss58/cwhook/oldstyledistributor43L.jpg

Remove the cap and rotor, both connectors, both screws.

There are two vent holes in the base, kinda tough to see when the distributor is installed, but you can feel 'em and put some compressed air to 'em. Gotta be clear, if not, that's why condensation builds up.

There's mention of the coolant temperature sensor and MAP sensor contributing to the problem too.
Do you still have your FSM to get values and check with a DVOM Eric?

Yeah, I checked the values on both and they are fine. I took off the map and cleaned the vacuum orifice, it was a little cruddy. I also drained off the gas and filled up with premium no ethanol gas and pulled the ignition module and cleaned and coated it with new compound and it still does it.

I broke down and called my dads mechanic, described the problem and he said "I know exactly what it is, bring it over in the morning." He thinks it's the ignition switch, not the key and tumbler but the electrical side of the switch that needs to be replaced. I'll let you know what happens.

Eric, Faulty ignition switch is a very common problem on the 2nd gen's, especially 97. Never heard of it on 1st gen S&T body but what the hell, I suppose it's possible. Let us know, I'm curious.

There was something about disconnecting the timing wire, like to set the initial ignition timing, to determine if the distributor module was bad. If after disconnecting it, the engine smoothed out meant the module was bad.

A bad module in my little '86 Cutlass Ciera w/Ponitac Iron Duke 4 cyl. caused similiar symptoms...the computer couldn't find #1 cylinder.

I just remembered, I knocked the knock sensor loose, right next to #5 sparkplug while changing sparkplugs...well it kinda fell apart when I got against it with the sparkplug socket. The clip wouldn't hold the pin in the little tube and the engine ran like crap until I held it in place with a stick.
You may remember this Eric, I used 3 sizes of vacuum line to hold it in place and still there today.

http://i131.photobucket.com/albums/p288/Clunk_/Image012.jpg

Well none of us were even close. Turned out to be the fuel pump relay cutting in and out when it got hot. Couldn't see it on the pressure gauge it was happening so fast, he found it with the scanner while the problem was happening. Not to bad, $12 bucks for parts and $40 for the diagnostic fees. My wife is making him cookies too.

Very good, we'll take that and add it to the trick bag.
Must be a pretty good scanner, do you know what brand?

Eric,
The relay shouldn't get hot. If the new one gets hot, check resistance in the circuits: grey wire should show less than 5 ohms from the relay to the pump. The black ground wire at the module should show less than 5 ohms resistance to ground. If those check out OK, check amperage draw on the pump, should be around 6 amps maximum.

Eric,
The relay shouldn't get hot. If the new one gets hot, check resistance in the circuits: grey wire should show less than 5 ohms from the relay to the pump. The black ground wire at the module should show less than 5 ohms resistance to ground. If those check out OK, check amperage draw on the pump, should be around 6 amps maximum.

Thanks for the quick post O.M. the problem is not fixed. It started surging and pulling after 5 miles on the drive home and stalled as I pulled into the driveway. I think we're looking at another fuel pump. I know how to check resistance but how do you check the amperage draw?

Also, I don't know if this is important but I noticed unusual wear on the cap and rotor I replaced, apparently the rotor is spinning off center inside the cap and wearing one side out. I don't know if this is because of cheap after market parts or if I have a problem with the distributor. The distributor was replaced awhile back, probably less than 50k. Picture below

http://i955.photobucket.com/albums/ae33/ericn1300/cap1.jpg

To check amperage draw on the pump: On your 92 Bravada, Set your DVOM on DC amps, stick one probe to battery positive and the other probe to the fuel pump prime wire. Read the amperage ;)

As for the distributor: There doesn't appear to be any damage to the terminals in the cap, just to the area next to the center. If that's correct, and the rotor was oriented properly to the distributor shaft, I'd say you need a new cap and rotor. If the bushings in the distributor were worn, the rotor tip would have contacted the terminals in the cap.

Maybe if you mounted the pressure gauge between the back of the hood and windshield, you could see what the fuel pressure does when the engine starts surging.

Maybe if you mounted the pressure gauge between the back of the hood and windshield, you could see what the fuel pressure does when the engine starts surging.

I didn't need to, i could watch the gauge as it surged and then stalled in the driveway. Very repeatable problem. The load leveler is driving it to and from work, about 1.5 miles each way and says it runs great for her so I'll let her use up some of the gas before I replace the fuel pump again. If it goes out on her for good she can use the walking for a change.

Good time to check the brake lines, fuel lines and wiring above the fuel tank.
I'm going to put some rust converter in a spray bottle and go under my stuff & spray.

Good time to check the brake lines, fuel lines and wiring above the fuel tank.
I'm going to put some rust converter in a spray bottle and go under my stuff & spray.

Good idea. That rust converter is good stuff, saved the floor pans on my 65 Mustang.

Still tearing my hair out over this one. I put in a new fuel pump, filter, relay and wiring harness. We have access to a Blazer with the same engine so we swapped the MAP sensor, the TPS sensor, the IAC, the EGR valve is clean and has a screened gasket, swapped over the ignition module, new GM cap and rotor, plugs and wires are a year old and it just purrs until it heats up.

When running on the scanner in road test mode the engine comes up to temp with the hood open, 197 degrees, then the scanner shows the ECM going into closed loop just as it starts surging and stalling. No trouble codes and all sensor values look good. Starting to suspect a bad ECM. Can we use the ECM out of the 93 Blazer for trouble shooting? The nearest ECM for a 92 Bravada is in the next state.

Also could the coil pack be causing it? It looks original, over 240k.

Can you swap O2 then maybe knock sensors?

You might be onto something with the O2 sensors. During warm up, the fuel system is in open loop. When it's in open loop the ECM ignores O2 sensor data. It uses TP sensor, MAP sensor and coolant temp data to determine which fuel mixture and ignition timing settings to use. The instant it switches to closed loop, if you have a lazy, (slow reacting) O2 sensor, it can definitely cause a surge in idle speed. O2 sensors react to fuel changes from rich to lean and from lean to rich. Over time and miles, the reaction time slows down. The faster it can react to changes, the faster the ECM can correct fuel mixture. It's possible for a sensor to be lazy in only one direction too. Usually it will set a DTC, but not always. It depends how close the parameters are programmed in the ECM. 02 sensors can be swapped around, there are some differences in wire length and electrical connector configuration so check them first before pulling the sensors out. If you have a scan tool with graph capabilities, you can dial in to each O2 sensor individually and watch it switch from lean to rich and back. Should be a symetrical pattern in both directions when it switches.

Might want to check for a vacuum leak too. In open loop the fuel mixture is richer which tends to cover up vacuum leaks. Once it switches to closed loop, fuel mixture leans out and if there's a vacuum leak, it can cause a lean surge. The surge would be more pronounced if there's a lazy O2 sensor involved.

That makes sense O.M. and in the past she has had an O2 DTC that comes and gos while freeway driving. I'll try swapping them out this week, Thanks.

Just a thought, because this happened to my '93 Bravada: check the VSS. If nothing else, pull the electrical connector, clean the terminals, fill with dielectric grease and clip it back together.

When it warmed up and was at highway speeds, it hesitated and choked. Every time, the speedo would flicker and jump.

The O2 sensor from the 93 won't work on the 92, going to have to go buy one. I think the 92 Bravada only has one O2 sensor, correct?

If I remember correctly there's just one in the pipe next to the transmission.

I agree, the system only needs one sensor. Mid '95 and older "W" engine only has one injector and it's batch fired so each cylinder gets the same fuel mixture. OBDI does not have the capability to monitor the catalyst so there's no sensor behind it.

Thanks Cris and O.M., I thought so since I only found the one. Going to buy a new one since there only $50, that's less than a tank of gas these days.

Still having the same problem. I put in a new O2 sensor and a reconditioned ECU with the old eprom.

I even tried disconnecting the temperature sensor to see if It would run in closed loop but that didn't work either.

Would that be the inlet air temperature sensor mounted on the rubber throttle boot?
Doesn't the knock sensor operate in closed loop too?
What about unplugging the gray wire for setting the initial ignition timing after the system goes into closed loop?

Running in closed loop didn't fix the problem, it's something wrong that the sensors are missing.

Here's a recap for everybody, the problem is drive ability, i.e. surging, pulling and stalling when the engine reaches normal operating temp. Current range is about 5 miles before it quits. No trouble codes set and running with a Sun scanner in road test mode identifies no problems.

So far I've changed or swapped all the below:

1. MAP sensor
2. TPS sensor
3. Ignition module, dist cap, and rotor
4. Fuel pump is new and at 60lbs, no leak down in over 10 mins
5. new fuel pump relay
6. new O2 sensor
7. checked all connections including the temp sensor and oil pressure sensor
8. Reconditioned ECM with the original EPROM


Two other mechanics I've discussed the problem with suggest that it's a bad catalytic converter, a blown head gasket or a cracked head, problems that only show up at temperature, which is hard to check. Doing a compression test on a hot engine is not much fun

If it's a blown head gasket or cracked head I might as well get a short block since the motor mount is broken too, and it has 249k miles on it now.

Anybody have any other Ideas off the top of their heads that would be simpler

Fuel/lean counts?

Could be cam sensor or crankshaft sensor.. Sounds like you tried everything else.

Running in closed loop didn't fix the problem, it's something wrong that the sensors are missing.

Here's a recap for everybody, the problem is drive ability, i.e. surging, pulling and stalling when the engine reaches normal operating temp. Current range is about 5 miles before it quits. No trouble codes set and running with a Sun scanner in road test mode identifies no problems.

So far I've changed or swapped all the below:

1. MAP sensor
2. TPS sensor
3. Ignition module, dist cap, and rotor
4. Fuel pump is new and at 60lbs, no leak down in over 10 mins
5. new fuel pump relay
6. new O2 sensor
7. checked all connections including the temp sensor and oil pressure sensor
8. Reconditioned ECM with the original EPROM


Two other mechanics I've discussed the problem with suggest that it's a bad catalytic converter, a blown head gasket or a cracked head, problems that only show up at temperature, which is hard to check. Doing a compression test on a hot engine is not much fun

If it's a blown head gasket or cracked head I might as well get a short block since the motor mount is broken too, and it has 249k miles on it now.

Anybody have any other Ideas off the top of their heads that would be simpler

i see you haven't change picup coil in dist. and it very well could cat or head gasket or head.

i see you haven't change picup coil in dist. and it very well could cat or head gasket or head.

the compression test came out normal, I think were looking at another new distributor. the current one was replaced 5 years ago and in one of my earliest post I included pics of unusual wear in the cap. A friend just happens to have one in his garage so we'll try that this week. I'll also take your advice and try swapping the coil pack since we have a parts vehicle available. Thanks.

It's been 5 years already? I remember that, good idea Eric, I saw a cracked starwheel/reluctor cripple a 305 Monte Carlo.

Finally got it fixed, turned out to be problem in the fuel injection wiring harness, a dealer only part, ouch.

Between the CPI and ECM/PCM?

Between the CPI and ECM/PCM?

Yeah, right about where it goes under the plenum. Might have been repairable but the whole thing was so brittle and we were not sure where the fault was so we just replaced the whole thing from the fire wall out. I also replaced the TPS which fixed the annoying miss when humid. Runs great now and the girls are happy to have it back in time for our camping trip.

Good work, I'll check mine next time I'm in there.
I disconnect that wire when I don't want the car moved.