1994 3.1L Stalling/starting trouble

[chagnobu]

Hope some of you can help here. I have been reading different posts with some similar issues for past four weeks, and tried some of the investigations and tests. The car has two symptoms that appear related. The first is after starting, cold, and sitting at idle for 3 to 4 minutes, the car stalls. Sometimes the stall includes a couple of surges, other times the rpms drop down a little and then it just quits. I can keep the car running indefinitely with a little throttle, about 1500 rpm. Once the car is warm, the stall happens in about 30 seconds after sitting at idle. The second symptom occurs during a start, and appears to be tied to the fact that the car just stalled. The car fails to start, it actually catches for a second, but then stalls instantly, like it is getting no fuel.

Things I have checked, I have pulled the tank, cleaned it, replaced the two screens on the pump and replaced the fuel filter. The pump runs well. I have jumpered the pump "on" with the car at idle, and it still stalls, so I don't think that it is the pump circuit. As the car runs indefintely at 1500 rpm, I don't feel it is the pump. That lead me to suspect the fuel regulator, which I replaced. I did find some small pieces of thread, like lint, in the screen of the old regulator, which seemed strange. The new regulator made no difference.

The battery connections are good, both were cleaned.

I have not pulled the OBD codes yet as I have not been comfortable enough with the car to drive it to Autozone.

The check engine light is on, and came on as part of this stalling/starting trouble. One other item of note, the "check guages" light is on, but is not always on. At 1500 rpm after 4 or 5 minutes, the "check guages" light went out, then on again, and flickered. All guages on the dash are normal during idle and at 1500 rpm.

Any advice would be appreciated.

[chagnobu]

Follow up info on my problems. I also removed the throttle body and cleaned it, removed the idle control valve and cleaned it, and removed the EGR valve/solenoid assembly and cleaned the openings. I have also done a vacuum sensitivity test, with the car running at idle, ...I have cycled the HVAC system several times, which appears to use vacuum to move the dampers, no effect on idle or the car running. Second vacuum test was to spray carb cleaner at all visible joints, no change in rpm or running.

I have not pulled the plugs and checked for signs of rich mixture in a cylinder, that's next. Also, plugs are new, replaced about 500 miles prior to the stalling starting issues. Performed the LIM gasket rebuild more than a year ago, and at the time cleaned the injectors by hand, and installed new O rings. LIM rebuild was about 4,000 miles ago.

Again, any advice would be appreciated

[rixGAphx]

It's tough to find somebody with the scanner and cable connector capable of checking your '94 (and '95's) codes, but that's what you need to do IMO.

Faulty temperature data, whether Inlet Air Temp (IAC sensor, in the air filter box) or Engine Coolant Temperature (ECT sensor, in the LIM below the t'stat housing), can easily cause an engine to stall.
Specifically, if the PCM thinks the engine is still cold ('cuz it's not getting correct ECT data) then it may make the idle mixture so rich that stalling is inevitable.

Then, have the fuel pressure tested.
Your old pump can easily have worn vane seals, that fail to produce adequate pressure even though the motor and vanes are spinning just fine.
This usually causes a problem at higher rpms, however, not down in the idle/low rpm range.

[chagnobu]

rixGAphx, thanks for the input, I will try to get the codes read and post them. Autozone has a scanner, I am just a little leary of driving a car that stalls at low throttle positions. I am still not ready to replace the pump because the engine runs so well at opened throttle positions. Is there any easy way to get the fuel pressure tested without buying the test rig and guage? Autozone doesn't have it as a buy/return/rental. Thanks again for your advice.

[chagnobu]

Problem solved. I broke down and bought an Actron scanner with the GM OBD 1 cable,$125 at Amazon. The scanner showed one code, 34, which is low output voltage from the MAP sensor. Checked the vacuum lines to the sensor, again, and the electrical connection, again, all appeared good. I purchased a new MAP sensor at Autozone for $48 and problem solved. Code cleared immediately, car starts and runs great. The $125 for the scanner and cable probably paid for themselves in one reading. Thanks again to rixGAphx.

[rixGAphx]

I broke down and bought an Actron scanner with the GM OBD 1 cable, $125 at Amazon.
The $125 for the scanner and cable probably paid for themselves in one reading.$125 is a good deal.
Do you have the Actron model number of the scanner and cable?

Glad you're back on the road again!
-Rick

[chagnobu]

Here's the order info from Amazon.com

1 of: Actron CP9145 AutoScanner Diagnostic Code Scanner with Live, Record and Playback Data Capability for OBDII (Post-1996) Vehicles
Sold by: Amazon.com, LLC
1 of: Actron CP9127 AutoScanner ALDL Cable Kt
Sold by: Amazon.com, LLC

[Notsonewguy]

hmmm, I have the same problem from the sounds of it...other than my check engine light has never came on because of it...the only real thing for me to test for is vacuum leaks and MAP sensor... can't afford a scanner at this time...but i did receive a code at one point..will post with more details tomorrow when i have acesss to one. I've changed and have tested the ignition wires, coils, plugs, Mass Air Flow sensor, EGR valve, IAC (tested fine with voltmeter seemed stiff but I dont know if its supposed to be, just looks like it should move slightly with a little ease, I dunno...) going out now to test out MAP sensor and whatever i can think of...I'm out a couple grand because of the work i've put in, the dealer is....AN IDIOT here, who claim they can't reproduce the problem to diagnose, but i can...EVERY TIME the car warms up, then comes the RPM surge, which almost always results in a stall. My fuel pump has been a little loudish (buzzing) always had that sound, but I dunno...running out of ideas...and money.. any suggestions are greatly appreciated . thanks guys

[rixGAphx]

hmmm, I have the same problem from the sounds of it...other than my check engine light has never came on because of it...the only real thing for me to test for is vacuum leaks and MAP sensor... can't afford a scanner at this time...
...going out now to test out MAP sensor.You've "changed..and/or...tested the EGR."
Have you actually removed the EGR valve and cleaned it and the passages it serves?

Even if the SES isn't 'on' at the moment, if it flashed on during the past week or so, you can still scan for inactive codes (since the 'puter stores them for about 30 on-off cycles of the ignition key).

Above all, the #1 cause of rough/surging idle in modern cars, when there's no SES 'on', is a vac leak of some kind.
Definitely check all the tubing, connections and devices. Spray some Winter Starting Fluid at them while the engine idles in 'P'; the rpm will rise and smooth when fluid is sucked thru the leak(s).

Good luck,
-Rick

[Notsonewguy]

Well its been a little while since my last post. Thanks for your response. I will definitely be checking all vacuum lines when i get a chance. Yes i have checked the EGR valve. bought a brand new one, installed it and exact same problem. I did clean up the area where teh gasket sits, but unfortunately same problem. Once again, thanks for the response, I'll post back after i test the vacuum lines.