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On cold start only, typically first start of the day, the car starts fine but as soon as the idle starts to drop the car stumbles and stalls unless you hit the gas pedal. Feels almost like it’s being starved for gas. When you restart it after the stall it fires right up and idles perfect. I’m to the the point where I believe the check valve may be shot in the pump??? car has 80k on it and pump is probly original. Would a faulty check valve cause my problem?? In the time I have owned the car I have replaced the plugs, wires, entire distributor, coil, Bosch III injectors from South Bay, FPR diaphragm, fuel filter, TPS and IAC. After injectors, fpr and tps car started much better but the lingering stall on cold start up is still there. Also checked for vacuum leaks with propane and found nothing and the PCV looks good as well.
Could be original, I was actually thinking of replacing it seeing as how they are not that expensive. Was debating on getting a delco or Bosch. You think that could cause my problem??
If it's not reading right then in closed loop its not going to add/pull fuel correctly. Unplug it, and start and run and see how it drives when the motor is warmed up. If it runs well in its default strategy because the O2 is unplugged, yet like crap with O2 plugged in then its most likely an old/bad sensor.
If you had a scantool of some sort you could also watch the O2 activity and see if it's pegged one way or the other.
I had a similar issue like yours. My car was running rough in closed loop usually in the first start in the morning. I replaces the O2 sensor with a Heated one and problem went away. Also with the heated O2 sensor my car went into close loop sooner and I felt it as it idle better.
Not sure if this is your problem, but might be a possibility.
Sac
Well today I unhooked the o2 sensor before starting and it fired right up and didn’t miss a beat, no hesitation or stalling just the check engine light lit up. I took it for a good ride and got it up to temp and still ran good, actually felt like it had a little more pep. I guess I need a o2 sensor, I was thinking of a Ac Delco pro from rock auto
I forgot the part number but get the 3 wire heated one. Ground the ground wire to whatever bolt is in the general vicinity of the manifold, and the power wire up to the fuel pump relay next to the brake booster. That's what I did and its running fine.
Update: Replaced the o2 sensor today and no more problems with cold start! The one I replaced was original and looked rough. Thanks again for the great advice.
UPDATE: It’s been awhile but wanted to update this in case someone has a similar problem, so after I replaced the O2 sensor the car did not have the stumble at start up for a little while but it came back rather soon. So when my car needed it’s yearly inspection I had my mechanic take a look at it and he determined it had a bad MAF sensor. The strange thing was that it really only acted up when the engine was warm (likely heat soak in the original 30yr old part) and caused the computer to dump more fuel and give it a smoky and rich start up when the engine was warm. The original problem was a secondary issue caused by the MAF as well because now it no longer wants to stumble and die after start up. I replaced it with a Delphi MAF from rockauto, was the best price I could find and is a quality part. Hope this helps someone, my mechanic said he’s never seen a MAF go like that.
It has been awhile since I’ve been on this thread but wanted to update on what I think may have finally cured the intermittent cold start and sputter/want to die. I have essentially been battling this intermittent issue since I bought the car and think I finally found the source…when datalogging,after getting a revised chip to delete AIR and EGR, I happened to actually start my data recording before starting the engine and was watching as I started the car and it began its sputter routine and I saw the fuel pump voltage dropped into the 5-6 volt range. Knowing that was not right I checked my wiring and relay for the fuel pump and quickly discovered this:
Pretty rough looking with loose/exposed wires
I also saw my connector tabs for the relay were broken. I can’t believe I missed this as I previously replaced the MAF relays. So after a new relay and a connector pigtail from Hawks I have not had this issue in over 2 weeks which is the longest I believe it’s gone without doing it. Hopefully this thread helps someone if they have a similar issue.
The factory grease runs down the wires and expands the wirecovering till it rips at the crimp. I clean it out with brake/carb/electrical cleaner, blow it out, pry open the crimp and gently pull the wire covering back up and recrimp.
