tom5170

Hi,

Car is completely stock and has 85k miles. Back in August the car randomly stalled right when I stopped at a stop sign near my house. A few weeks later it stalled again at the same stop sign. So I took the TB off and cleaned every square inch and made it nice and shiny. A few weeks later the car stalled again - I again cleaned the TB 3 more times. This didn't help at all so I replaced the spark plugs, replaced plug boots, cleaned the MAF sensor, cleaned the MAP sensor, ran techron in the gas and a few other fuel injector cleaners and all this still didn't help. I did a compression test and all 4 cylinders are reading 180 psi across. I unhooked the brake booster and did a cigar vacuum leak test and didn't see any smoke any where. I also sprayed carb cleaner everywhere on the engine where a vacuum leak would be possible. I can feel shaking sitting in the drivers seat at idle and its worse when the AC compressor is on. THERE ARE NO CHECK ENGINE LIGHTS AND THERE ARE NO PENDING CODES. The car never starts hard. It doesn't have any loss of power. The transmission shifts normal. I have a bluedriver bluetooth scanner and my STFT and LTFT appear normal - it doesn't appear the cars running rich or lean.

There is a pattern though: It only does this on the first start of the day. And it only happens a second right after I'm stopped. Sometimes the engine will just stall or sometimes the RPM's will dip and I can feel a jerk and the engine stumble but then it smooths back out to 700-800ish. After 10-15 minutes of driving the car will stop and go all day and operate normal. The shaking/vibrating at idle also seems to clear up a little too. I can start the car on a cold engine and rev it and let the rpm's go up and down and it never stalls or stumbles, it's only when the vehicle is in motion and then stopped.

Maybe someone can help me? I have the scan tool. Maybe someone can tell me which data to log on it? I'm new to OBD2 scanners and reading data lol. I have a data log from earlier today when the car stalled out 4 seconds after I was stopped - The STFT went to like -17 as the RPMs dropped and the control module voltage was at like 12V then went down to 11V. This was at the first start of the day and after driving 10 minutes it drove normal for 40 more minutes.

tom5170

So today I pulled the fuel rail and the ends of the injectors weren't dirty looking or clogged at all. I ended up cleaning the injectors with carb cleaner anyways. I used a 9V battery and some wire to pulse the injectors. I put electrical tape around the end of the straw to the can of carb cleaner to make a pressure tight seal when I insert the straw into the injector and spray. After I kept spraying carb cleaner through I pulsed the injector. Then I "back flushed" too by putting the straw at the other end where the fuel sprays out and pulsing the injector. I did this to all the injectors. I then put everything back together and checked the spray patterns by turning the key and holding cardboard to them - the spray patterns all looked normal. I also didn't see any of the injectors leaking. Needless to say this didn't fix anything and the car STILL shakes a bit when cold and clears up some after it runs about 10 mins or so. So I guess I can rule out the injectors as being faulty. All of the o-rings and cups looked good so I just reused them.

jdbaugh1

iTrader: (1)

I doubt it's your injectors. Are you reading the STFT and LTFT at idle? Also, check the MAF sensor reading at idle in g/s. Use your scan tool to see what the MAP sensor is reading at idle.

bahoodle

start the car up in the morning and grab the crankshaft position sensor harness and yank it a couple times. if that connection is loose it will die and run poorly.

tom5170

What should my maf and map readings be? I have no idea what is a good or bad reading, etc lol.

My fuel trims always appear close to 0 at idle. Even on cold start. Usually within -5, 5 both stft and ltft. I do have a data log a few days ago from when the car stalled and the stft went to -16 the second it stalled, ltft was around 3. I don’t think I had the maf or map logged then. I believe my absolute throttle position dipped to 16% at stall, it’s usually around 20% at idle.

tom5170

Would this cause the cold engine stall issue? It only happens on first start of the day and it doesn’t randomly die... it only does it when stopping at signs/lights lol. My 3.8 series 2 had a bad CPS and it would randomly stall or crank no start randomly lol.

This car fires up just fine though.. doesn’t start hard at all. Idk... sometimes I think maybe I got some sticky valves or something lol. I threw some marvel mystery in the oil and gas lastnight.

cobaltss#01

iTrader: (4)

What about vacuum lines. Like the one for the brakes?

jdbaugh1

iTrader: (1)

I went back and reread your first post. It appears you have an automatic transmission? When you say your car is shaking at idle and your stalling issue ONLY happens when coming to a stop, specifically the first stop of the day, it makes me think this may be a torque-converter or transmission issue. You say the problem goes away after everything warms up and even the shaking fades. If it is a TC or trans issue it could be amplified by cold viscous transmission fluid then once it warms up and thins out the problem fades. Is the problem any worse when it is colder out? I'm not familiar with the Cobalt's automatic transmission at all really but all modern automatics have a locking torque converter for fuel efficiency. I wonder if your torque converter is not properly releasing or is otherwise dragging more than it should.

The next time you are coming to your first stop of the day (or when you would normally have the issue) shift the transmission into neutral before slowing to a stop. See if the shaking and stalling issue goes away.

chris88z24

Clean your throttle body.

tom5170

I’ve pulled this line off and put it back on. I also sprayed it all over with water and carb cleaner and squeezed it.. couldn’t find a vacuum leak lol.

tom5170

Yeah it’s auto. I had the shift solenoids replaced in July cuz solenoid b failed and I couldn’t accelerate past 40. It first stalled beginning of August. The invoice just says 2 shift solenoids. They didn’t really say how the solenoid failed just that it was the solenoid and they replaced both. I have 3-4 gear again and the trans shifts good through all gears. I did replace the ground terminal on the trans stud that grounds the tcm when I was trying to figure out my solenoid issues before I took it to the trans shop.

Ill try the neutral thing next time. The car actually stalled today first start of the day 1.5 miles from my house at a light and after that I had no issues.

the shaking seems to clear up a bit after I’ve been driving for a while. If I turn the car off a few minutes and back on I can feel the shaking a little more but not as bad on a cold engine. If I drive again for a while the shaking is less once again. The shaking feels like a miss or something... just a constant shake. It’s at idle only

tom5170

i do mainly city driving nothing over 45mph 80% of the time, 50mph is usually the most. and I live in a residential neighborhood 25mph speed limit.

Like I said the car will stall out right after I stop and sometimes the rpms will drop around 400-500 and I can feel the engine stumble but then the rpms will go back up to 700 and run normal. Sometimes the stall or rpm drop will occur 3-4 seconds after being stopped. And this happens only on the first start of the day.

Yesterday I started the car for first time of the day and I let it idle while I sorted pop bottles in the trunk and it took me about 10 minutes and when I jumped in and drove off I had no issues when stopping. My coolant temp usually reads around 190-194.

tom5170

I went to auto zone and grabbed a loaner fuel pressure tester kit.

At idle its at 60psi. At higher rpms it stays at 60psi. The gauge does flutter really fast but flutters at 60... is this cuz the fuel injectors are pulsing? When shut off it goes to 50 psi and stays at 50 until 10 mins later and then it goes to 48psi.

Seems like I got good fuel pressure?


i also tried the converter test a few times by putting my foot on brake and flooring the gas. The rpms maxed out around 2500ish. When I let off gas the rpms dropped to 800 and it didn’t stall. I did this a bunch of times. Maybe I will try it when the engine is cold

tom5170

Yesterday I was sitting in driveway hot engine idling in park and randomly revving watching rpm gauge. I was able to make the rpm go from 3000 down to 800 then in a split second it dropped to 400 and I felt the engine stumble and then it jumped right back to 800.

also, I have a high pitched tapping noise from passenger area. The noise goes away after 45 seconds and it happens anytime the car sits for a few hours. Can it be the exhaust manifold? Could this be causing the stalling issues since it’s before the primary o2?? It sounds EXACTLY like this noise in this video:

bahoodle

sounds like your timing chain tensioners done

tom5170

I actually found 2 loose nuts on the exhaust manifold. I tightened them up and now I have no more ticking.

I don't hear any chain noise or any other noise now on startup now

bahoodle

u have a lsj with an automatic transmission?... lol

tom5170

06 ls 2.2 with auto trans.

i don’t know what the hell is wrong with this car lol. I do know that I have no more ticking noises since I tightened the manifold studs.

It was snowy and 24 today. I had the car running for a while to warm up and when I put it in reverse and backed up 3 feet not even 2mph and stopped, right when I stopped the RPM dipped to 400, and jumped back up to 800 and idled normal. It’s weird cuz after I drive for a while it goes away. I cleaned tb a bunch of times lol.