Set of issues after vacuum leak

[LilyAnna]

Sooo... here’s the deal. 2013 LFX auto trans, no mods:

I had 2 injectors stuck open, replaced them. Then I had a vacuum leak due to an intake manifold gasket being worn out and since then she hasn’t been quite well.

Things I’ve identified:

1. Cranks and turns over with no struggle when “cold” aka sitting overnight (no snow, rain or cold weather whatsoever right now), but RPM needle bounces up and down a bit (aprox 150rpm fluctuation) as if trying to adjust RPMs when “cold” instead of revving higher and steadily lowering RPMs as it warms up. Also the engine feels shaky, shakier than I believe it should for this warm weather.

https://youtu.be/wzXm6Yjg--0

2. The 6 spark plugs had dry soot/carbon on the tips (see pic).

3. Since that vacuum leak RPM needle doesn’t seem steady when idling (+/- 50 rpm fluctuation) that some have told me its normal but to be honest I didn’t notice that before these series of unfortunate events.

4. This is the fun part (sarcasm). Some times when trying to start the car after a drive NOT after sitting overnight. I randomly get a weird start as if the starter is engaging but the engine can’t quite turn over but if you give it a little gas then she fires up (hasn’t failed to start yet). This random hard start has happened after driving it for a short distance, long distance, highway speed, city speed, after reaching operating temp. The annoying part to this is I can’t figure out a pattern so I know “oh ok it only happens when I drive short distances or you name it” it has happened about 10 times and there’s no common denominator.

5. No CEL or permanent codes stored

6. Throttle response is good, response under load is good, performs well on the highway and high or low RPMs (except for the tiny annoying bounce at idle)

Since point number 4 is so random and sporadic I haven’t been able to get it on camera.

Recently I’ve just had the throttle body cleaned and all 6 spark plugs replaced with ACDelco’s. (No negative nor positive effect on issues described above)

Could that relate back to the vacuum leak? Something not sitting well after the intake manifold gasket replacement?

I don’t have the right tools to go inspect that myself but what does this sound to you? Also I cant take her to the shop now due to covid-19 restrictions

Sorry for the long post, I wanted to give as much detail as I could...

Please ask away anything else you’d like to know!

Thank you

[Rock-It Man]

You mentioned the intake manifold gasket getting replaced. What symptoms led to the diagnosis that it needed to be replaced? Same symptoms as now?

I would be looking there again. Improper installation? Damaged intake manifold?

[LilyAnna]

Originally Posted by Rock-It Man

You mentioned the intake manifold gasket getting replaced. What symptoms led to the diagnosis that it needed to be replaced? Same symptoms as now?

I would be looking there again. Improper installation? Damaged intake manifold?

Drove it literally once after I got it back from the new injectors and as I was driving back home the car felt heavy as in poor acceleration and as I was pulling into my driveway it stalled. My husband drove it back to the shop (2 blocks away from home) and he had to keep it revved up so it wouldn’t stall.

Those were the only “symptoms” as we took it back right away, the mechanic called and told us it was the gasket. I just drove it once before having to take it back so there was no time to discover other symptoms as you simply couldn’t drive the car. Before this bs the car was flawless.

I know, why didn’t you just take it back to the shop? We did but since there’s no CEL or stored codes the mechanic didn’t want to take the car in, he’s getting of age and can be so stubborn, we’ve know him for years. No excuse as we’re paying for a service but we just want to give someone else a shot, we’re trying a new mechanic anyways.

[CamaroBarb]

Sounds like a injector or a few are leaking. I'd pull all the plugs, lay them out in the order they come out and compare them. The leaky ones are going to look dark.

[acutron42]

Check to make sure your air box & all air intake components are sealed up correctly if it is stock. This sounds strange but when I bought my 2013 2SS the idle did the same thing. It drove me nuts until I found a broken tab on the air box. No cel, just ran like crap. All is fine now.

[LilyAnna]

Originally Posted by CamaroBarb

Sounds like a injector or a few are leaking. I'd pull all the plugs, lay them out in the order they come out and compare them. The leaky ones are going to look dark.

Pulled the plugs about 2 weeks ago and all 6 looked like the pic I attached, all 6 have been replaced (I didn’t change them back when I had the 2 stuck open injectors). Also, all 6 injectors are new.

To consider regarding the spark plugs: The car is used for short trips mostly, city use and its not my daily driver and we all know what that can do to spark plugs

[LilyAnna]

Originally Posted by acutron42

Check to make sure your air box & all air intake components are sealed up correctly if it is stock. This sounds strange but when I bought my 2013 2SS the idle did the same thing. It drove me nuts until I found a broken tab on the air box. No cel, just ran like crap. All is fine now.

Thanks for the idea but air components are sitting correctly and properly adjusted

[acutron42]

Mass airflow sensor dirty? It does seem like a vac leak though.

[LilyAnna]

Originally Posted by acutron42

Mass airflow sensor dirty? It does seem like a vac leak though.

Haven't checked the MAF yet, worth taking a look at it as it would mean a simple/cheap fix.

I'll keep y'all posted, meanwhile, all ideas are welcome.

[xstuntman]

I would get a fuel pressure check just for fun.
Those high pressure pumps do weird things.

[acutron42]

Originally Posted by xstuntman

I would get a fuel pressure check just for fun.
Those high pressure pumps do weird things.

If all 6 plugs look the same & no cel, both banks are suffering the same problem. Maybe some water in the fuel?

[LilyAnna]

Originally Posted by xstuntman

I would get a fuel pressure check just for fun.
Those high pressure pumps do weird things.

I had that thought on my mind but was on denial bc of the cost and also, wouldn’t I have issues at high speeds? I took it on the highway yesterday, up to 100mph and boy did it felt good as ever, uphill as well. Do you know how many psi is a good read?

[LilyAnna]

Originally Posted by acutron42

If all 6 plugs look the same & no cel, both banks are suffering the same problem. Maybe some water in the fuel?

Hmm highly doubt it, I’ve gone through a few tanks already and 3 different brands since then.

[acutron42]

This is strange without even a random misfire or other generic code considering it stalled. Is the pcv system in check? It seems like one stupid problem. Someone here will have an answer.