Starts but dies [FIXED]

2000 Chevy Malibu 3.1. 240k miles

Redid head and intake gaskets, replace crank sensor as well as Pcv valve with duralast brand. Pcv was clogged and crank sensor got messed up when redoing front seal.

Sluggish to start unless foot is on gas pedal. Foot needs to be on pedal to stay running.

Thought it may have been an issue with the Iac. Removed valve and motor Steps, tried a second Iac laying around but no change. Left Iac removed but plugged up. Start engine, runs, poorly, without foot on pedal.

Fuel pressure is 50 psi key on. Can't tell what it is while engine is running as there aren't two of me

Any ideas?

Dirty throttle body?

pole71 wrote: Dirty throttle body?

All intake components while removed were thoroughly cleaned and most if not all carbon deposits were removed so I don't think that's the issue

What was the complaint before everything was replaced? Check for exhaust full of coolant if it was burning a lot of coolant. Remove o2 sensor and see if it will start.

gav09 wrote: What was the complaint before everything was replaced? Check for exhaust full of coolant if it was burning a lot of coolant. Remove o2 sensor and see if it will start.

240k on car. Decided it was time for gasket change as engine had issue with external/ internal coolant loss. Did head gaskets since I was already there. Car was burning coolant for 100k+ miles.

Ill see what happens

Hey Donnie,
Glad to hear you got the parts you needed to get it running.
Any popping out of the intake or back firing, or anything like that?
I would start with a cheap, simple vacuum gauge.
A steady needle on the vacuum gauge would prove that every thing is good in the valve train.
A dropping gauge would indicate a cylinder (s) not sealing well.

I'm by no means implying you messed anything up during reassembly, this is just a good, simple test to get an idea of the integrity of the engine. Anything wrong here and all the sensors and solenoids in the world won't help it run any better.
I've seen professional mechanics change coil packs, modules, crank sensors and everything else under the hood because they never thought the valve train could be to blame.

Noah wrote: Hey Donnie,
Glad to hear you got the parts you needed to get it running.
Any popping out of the intake or back firing, or anything like that?
I would start with a cheap, simple vacuum gauge.
A steady needle on the vacuum gauge would prove that every thing is good in the valve train.
A dropping gauge would indicate a cylinder (s) not sealing well.

I'm by no means implying you messed anything up during reassembly, this is just a good, simple test to get an idea of the integrity of the engine. Anything wrong here and all the sensors and solenoids in the world won't help it run any better.
I've seen professional mechanics change coil packs, modules, crank sensors and everything else under the hood because they never thought the valve train could be to blame.

No back firing or intake popping. Just starts then dies as quick as it started. Throttle needs to be slightly open or rough starts. Runs otherwise smooth when you steadily gas it.


A vacuum test crossed my mind but the car not idling won't allow for vacuum test?

Yeah, a running vacuum test might be weird, but it'd definitely be worthwhile to know if there's excessive cranking vacuum.

Seeing high vacuum in the intake during cranking would suggest a breathing problem, and point your focus towards the intake. The fact that you have to open the throttle to get it to idle kinda says that, too, but it'd be nice to back it up with a gauge reading.

I'm thinking of this two part series. Not saying your IAC is stuck closed (we know it isn't), just referencing the technique to others:

How long was this vehicle down for? Some cars act real stupid to run after being down for a while.

Just in case I'd throw a leak down test at it.

Tyler wrote: Yeah, a running vacuum test might be weird, but it'd definitely be worthwhile to know if there's excessive cranking vacuum.

Seeing high vacuum in the intake during cranking would suggest a breathing problem, and point your focus towards the intake. The fact that you have to open the throttle to get it to idle kinda says that, too, but it'd be nice to back it up with a gauge reading.

I'm thinking of this two part series. Not saying your IAC is stuck closed (we know it isn't), just referencing the technique to others:

For this cranking vacuum test I'm looking for a reading of 3-5 on the gauge? Sometimes watching all these addicting scanner Danner videos I forget basic operational tests

Caritech wrote: How long was this vehicle down for? Some cars act real stupid to run after being down for a while.

Just in case I'd throw a leak down test at it.

It was sitting for a little over a month. You need air source for a leak down test right?

Hurs a good ole cranking vacuum test



I can't find much information on the internet regarding cranking vacuum tests. Only what specified range should be. Does the fluctuating needle speak of anything? Wish I had you guys knowledge Base. I'd be done with this thing in an hour or two instead of weeks.

After hours upon hours of gazing at the engine.. Wondering what my next step will be, considering all the possibilities as to avoid defeat.

1. Exhaust restriction ( last checked when car running PSI in normal range) ( still no start even with O2 sensor removed)
2. Ignition issues ( getting spark)
3. Fuel delivery issues( Maybe losing pressure at idle?)
4. Charging issues ( getting nominal charging voltage when I can get it to run)
5. Compression issues ( can one cylinder with lower compression allow an engine to completely die of no throttles given?)
6. Idle issues ( car can start without throttle open if Iac valve is removed - runs poorly)
7. No coolant in system yet ( need to Flush dexcool sludge out- wanted to. Verify operation first before dumping in liquid ) I've heard of engine computer using temp as a means of regulating idle speed.. does there need to at least be some liquid in the system?

Car needing a throttle push would indicate some sort of restriction or a failed Iac? Just trying to get a visual and understanding more than anything

Sometimes the most elaborate of issues can be due to a simple fix. In this case I realized after standing there that I was using the wrong throttle body gasket as it was covering the idle air valve port.

Disappointed it took me ages to figure that out

I

Donnyten wrote: Sometimes the most elaborate of issues can be due to a simple fix. In this case I realized after standing there that I was using the wrong throttle body gasket as it was covering the idle air valve port.

Disappointed it took me ages to figure that out

Could happen to anyone. Just blame the parts guy.

Donnyten wrote: Sometimes the most elaborate of issues can be due to a simple fix. In this case I realized after standing there that I was using the wrong throttle body gasket as it was covering the idle air valve port.
Disappointed it took me ages to figure that out

Good eye! Glad you found it.

Hey, nice! Don't feel too bad about that, man, it happens.

Thanks for doing that cranking vacuum test, though. I really expected it to read higher than 5" with the IAC port blocked... Maybe 5" is actually too high? :huh:

So, she runs and idles now?

Donnyten wrote: I can't find much information on the internet regarding cranking vacuum tests. Only what specified range should be. Does the fluctuating needle speak of anything? Wish I had you guys knowledge Base. I'd be done with this thing in an hour or two instead of weeks.

I really like this idea. I mean, I have NO idea how we'd go about making one, but I think it'd be valuable to forum members.

Thanks fellas.


Yep. She's good now. Idles well. Need to Flush all the oily dex sludge crap that's lodged in the block next. Unfortunately it's still leaking oil from the front bank head gasket area and lower intake mani areas

I disabled the fuel and ignition in that test, as I read was the correct thing to do.

Also, there definitely was some intake backfiring( popping) going on at some point through all this.. When I realized at one point the engine started and ran horribly on a vacuum leak..

Would it be worth while checking out the valve train/intake manifold gaskets again? Or would a steady vacuum reading in the green be enough to say all well for now?

As long as the needle is steady and not bouncing or dropping off, the valve train should be fine.
Sorry to hear about the oil leak after all that work! Any ideas?

Noah wrote: As long as the needle is steady and not bouncing or dropping off, the valve train should be fine.
Sorry to hear about the oil leak after all that work! Any ideas?

I hope things aren't warped.. Other than that why else would I still have leaks seeping from the lower intake and headgasket areas? Torqued to spec in correct order including the degree turn at the end