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Discussion Starter #1
I honestly don't know what's going on and it's getting slightly irritating now. For the past two years since December 2017, my car likes to buck like it wants to take off by itself when sitting at a light and idling. The list of things I have done to try and fix this problem is:

Replace MAF sensor
Clean the throttle body
Replaced the throttle body with a used one
Replaced spark plugs
Replaced coil pack
Replaced Brake booster and hose
Replaced intake snorkel that attaches to throttle body to air box (4 times)
Replaced intake manifold gasket(twice)
Replaced valve cover gasket
Replaced TCM (that actually failed though lol)
Replaced PCM and ECM combo
Replaced Fuel Pump (twice, never ever buy GMB brand fuel pumps ever again. Sticking with OEM)
Replaced Fuel filter
Replaced Fuel injectors
Replaced Purge Valve solenoid
Replaced MAP sensor with a used one
Also replaced both O2 sensors and catalytic converter with ZZP downpipe and cat combo.

I'm honestly lost with what in the world is going on with my car and I refuse to give up because I love it so much. After I replaced the Fuel pump my hesitation under acceleration had stopped and I'm finally getting the correct mpg my car is supposed to have and long term fuel trim is between -3 to -12. Anything would help. Thank you for taking the time out to read my post!
 

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Is it throwing any codes? CEL on at all?

I can't think of much more to check other than transmission, PCV system entirely... He'll, even low refrigerant on the A/C as that can cause the clutch on the compressor to engage/disengage causing a similar effect.
 

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Discussion Starter #3
Surprisingly no DTCs. It used to throw p0442 and p0172 but I replaced the fuel pump which was causing my car to throw p0172, but, P0442 just went away by itself. What would cause the transmission to make these symptoms occur? What park of the PCV system would cause a vacuum leak to do this? Lol I wouldn't be surprised if my A/C was causing it, but it blows pretty cold, especially when the car has been running for like 5 mins. Also thanks for the quick reply!
 

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Clutch slip. Converter slip. Surging when it re-engages. Transmissions are very... Interesting on how they behave when they're having issues. Varied. Might not even be that, but I've experienced surging with a bad transmission.

As for the PCV/Vacuum, well, anything. Loose hose, loose fitting, cracked assemblies... Only real way to know is to put a gauge somewhere in the vacuum system and see what it does.
 

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Discussion Starter #5
Would a transmission low on fluid also cause it? And I checked my crankcase hose and it might be the culprit but, I'm going to buy a new one and see if that fixes it. Because I've replaced basically everything but the transmission and the engine itself. lol
 

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I'm not the authority, I only speak from experience... But it could be. There's so many other little things that it can theoretically be that... Well... Yeah.
 

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Discussion Starter #8
Thank you everyone for your replies! Quick question though but, can a massive exhaust leak cause this problem?
 

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Discussion Starter #10
Okay that makes a lot of sense because yesterday on my way back home, my exhaust manifold made a huge exhaust leak and made my car sounded like a pissed off lawnmower lol
 

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I have the same issue, spent hours searching online for answers and am trying to make peace with it since it's the new normal. But I understand why the poster has a passion for their car and wants to solve the problem.

I've had the 2008 Cobalt LS for ten years without it ever breaking down or leaving me stranded. It has saved me a lot of money in not having a car payment. I bike a lot and every day I hear cars and trucks that are newer and worth more that sound bad. Mine isn't embarassing to drive around in at least. The idea of 'upgrading' to a less reliable car scared me.

Mine started doing this after I had an independent mechanic replace my timing chain. CEL came on and code was a timing issue, I drove it in to the mechanic closest to me, tensioner was broken but the chain was not. I have brought it back twice and they can't figure it out. It accelerates fine, drives in high speeds fine, but as soon as I decelerate or stop it starts doing the same thing. It also takes longer to start on a cold start which it didn't before.

I read a post and saw a Youtube video of two people who had the same issue immediately after a timing chain replacement and never saw a solution.

At night when it pulsates at a stop the lights go dim. It will not do this if I have the fan going full blast, the power will drop for a split second and bounce right back, no pulsating.

My plan is if it stays reliable I will drive it into next year always with the fan full speed and the temp gauge spun to match the season and treat the $1400 as car payments I would have made had I got nickles at trade in or scrapped it.

I must add I rented a Camry for a week and other than road noise (HUGE difference!) and rattles, my car compares fine with it and every other releatively new car I've rented. Mostly highway mileage is still mid to high twenties with the fan at full blast.
 
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