q45 Stalling/Dying

[pilot_456]

So I just bought a q as a parts car for my swap. But I wanted to drive it around and get it running nice and healthy before doing the swap.
It turns on fine and idles fine until it warms up.
Then the idle fluctuates and it will stall. When driving it will run fine at a constant throttle, if I stomp on it or let go of the throttle it will stall as well. I just replaced the MAF so it is not that! Would it be the IAC? I know that there are lots of similar threads to this one. Most of them point to the MAF as the culprit.
Help please!

Here's a video of the stalling/rough idle
[youtube]http://www.youtube.com/watch?v=TgEHYSPggwE[/youtube]

And on the part with the odometer showing it was fluctuating by itself.

[N/A Q45]

Sounds like it is leaning out. (Vacuum leak, maf/maf signal) unplug the maf and then see if it idles better. That's the best way to test one as chances are that if you got one that isn't brand new it could still be causing problems.

[pilot_456]

Sounds like it is leaning out. (Vacuum leak, maf/maf signal) unplug the maf and then see if it idles better. That's the best way to test one as chances are that if you got one that isn't brand new it could still be causing problems.

I did do that, nothing changed.

[rabsusa]

hi

try cleaning intake runner, the idle control valve on the back of the plenum and the sensor inside the air box with carb cleaner for starters, any fluc idle is issue with ICV or its related plumbing - in my case tube had come undone that connects to the bottom of ICV; what is idle rpm??

Rob

[N/A Q45]

Sounds like it is leaning out. (Vacuum leak, maf/maf signal) unplug the maf and then see if it idles better. That's the best way to test one as chances are that if you got one that isn't brand new it could still be causing problems.

I did do that, nothing changed.

Well I'd say you found your problem maybe. I know whenever I unplug a maf the engine kind of hiccups as it goes into limp mode. It should either run worse or better if the maf is unpluged. Definitely not the same.

[pilot_456]

Well I'd say you found your problem maybe. I know whenever I unplug a maf the engine kind of hiccups as it goes into limp mode. It should either run worse or better if the maf is unpluged. Definitely not the same.

Well if I unplug it I noticed it will definitely die faster.

And the idle rpm is around 1k, 800 when cold then it just starts fluctuating when cold.and I will try that thanks rob!

[N/A Q45]

Well I'd say you found your problem maybe. I know whenever I unplug a maf the engine kind of hiccups as it goes into limp mode. It should either run worse or better if the maf is unpluged. Definitely not the same.

Well if I unplug it I noticed it will definitely die faster.

And the idle rpm is around 1k, 800 when cold then it just starts fluctuating when cold.and I will try that thanks rob!

Well when you unplug the maf the ecu gives the engine alot more fuel. On my car I can drop the fuel pressure to around 45psi and it will never idle because of how lean it is (wide bands show full lean) but when I unplug the maf at the same fuel psi it runs very rich (10.5ish on the wide bands) so if you unplug it and it gets worse that makes me now think it is running too rich. Which could be a number of things, first thing I would do now is check for codes.

[OwnerCS]

Hey neighbor. I wish you were a little closer as I have the handheld diagnostic (ECUTalk) computer and other tools to give it a check out. It sounds like classic MAF -- I usually keep a spare (test working) that I pick up from a salvage yard. However as N/A Q45 pointed out, it could be many other things. I've found more bad MAFs on the VQ30DE. After replacing the MAF with a known good part, I usually start with pulling the codes, plug readings (for non-firing), injector testing, IACV - EGR cleaning and testing, vacuum leak testing.

If you don't find an answer, I'm planning a trip to Tarrant County in about 3 weeks in my 91 -- that is if I get my A/C fixed.

[pilot_456]

Well when you unplug the maf the ecu gives the engine alot more fuel. On my car I can drop the fuel pressure to around 45psi and it will never idle because of how lean it is (wide bands show full lean) but when I unplug the maf at the same fuel psi it runs very rich (10.5ish on the wide band's) so if you unplug it and it gets worse that makes me now think it is running too rich. Which could be a number of things, first thing I would do now is check for codes.

Correction, when I unplugged it, it did run better. It was blowing black smoke so running rich like you said and it didn't die/stall. So what could it be a bad connection or plug on the MAF? Because it is new! I know for a fact that it is.

[pilot_456]

Hey neighbor. I wish you were a little closer as I have the handheld diagnostic (ECUTalk) computer and other tools to give it a check out. It sounds like classic MAF -- I usually keep a spare (test working) that I pick up from a salvage yard. However as N/A Q45 pointed out, it could be many other things. I've found more bad MAFs on the VQ30DE. After replacing the MAF with a known good part, I usually start with pulling the codes, plug readings (for non-firing), injector testing, IACV - EGR cleaning and testing, vacuum leak testing.

If you don't find an answer, I'm planning a trip to Tarrant County in about 3 weeks in my 91 -- that is if I get my A/C fixed.

I think my uncle has a diagnostic tool so ill try and see what codes its throwing, but if I can't find someone with the tool ill let you know thanks! Ill probably end up doing all those to find the problem as well.

[N/A Q45]

Well when you unplug the maf the ecu gives the engine alot more fuel. On my car I can drop the fuel pressure to around 45psi and it will never idle because of how lean it is (wide bands show full lean) but when I unplug the maf at the same fuel psi it runs very rich (10.5ish on the wide band's) so if you unplug it and it gets worse that makes me now think it is running too rich. Which could be a number of things, first thing I would do now is check for codes.

Correction, when I unplugged it, it did run better. It was blowing black smoke so running rich like you said and it didn't die/stall. So what could it be a bad connection or plug on the MAF? Because it is new! I know for a fact that it is.

If unplugging the maf it runs better = it was too lean
If unplugging the maf it runs worse= it was too rich
So just check that the maf is working test its volts at idle if you can keep it running by back probing the white signal wire, check the pins in the connector for the heck of it but it just sounds like the maf or a vacuum leak. But that would take one heck of a vacuum leak and I'd think you would be able to hear it clearly.

[N/A Q45]

One last thought, maybe the egr is stuck open. I would test that as well.

[black g50]

Any updates? This happened to me twice last month after sitting in parking lot shopping.She would fight to stay running,gave up and let it sit longer then everything was fine.When I disconnect maf my car shuts off?

[pilot_456]

One last thought, maybe the egr is stuck open. I would test that as well.

The previous owner is having the car towed to my house next week so I'll make sure to check all of the things you suggested thanks N/A!

[pilot_456]

Any updates? This happened to me twice last month after sitting in parking lot shopping.She would fight to stay running,gave up and let it sit longer then everything was fine.When I disconnect maf my car shuts off?

I'll update you next week once I get a chance to work on the car.

[black g50]

Sounds like it is leaning out. (Vacuum leak, maf/maf signal) unplug the maf and then see if it idles better. That's the best way to test one as chances are that if you got one that isn't brand new it could still be causing problems.

Do you unplug maf while car is running? If so car turns off,is this normal? Car is running lean but no vacuum leak found. Maf replaced but still did the same thing in video. Everything at connection snug,some slight rubber cracking on connector but doesn't look to have gone through.

[N/A Q45]

Sounds like it is leaning out. (Vacuum leak, maf/maf signal) unplug the maf and then see if it idles better. That's the best way to test one as chances are that if you got one that isn't brand new it could still be causing problems.

Do you unplug maf while car is running? If so car turns off,is this normal? Car is running lean but no vacuum leak found. Maf replaced but still did the same thing in video. Everything at connection snug,some slight rubber cracking on connector but doesn't look to have gone through.

If it turns off try and start it. Then see how it runs. Sometimes if the shock of unplugging the maf is bad enough it will stall at first.

[elwesso]

Some iffy advice here, so let me try and clear some things up.

First, did you replace the MAF with a used one? A used MAF is usually a good bet, but it's still possible you got a bad one. When the car is idling, if you jiggle the connector, does the idle change? If so, you probably need to clean the connector and bend the pins a little bit so it gets a tighter connection. If no change, then it could be the MAF itself.

Also, no word on fuel pump replacement. If the fuel pump is noisy you definitely want to change that first and foremost. I've seen some weird things happen with a bad fuel pump, so if there's no confirmation on it being replaced I'd replace that FIRST.

Usually EGR valves don't get stuck open, the passage between the EGR valve and the plenum gets coked up so the EGR won't work.. All you have to do is lift up on the EGR valve and see if the engine stalls. If it does, then you know you're getting some flow through the EGR.

[N/A Q45]

Some iffy advice here, so let me try and clear some things up.

First, did you replace the MAF with a used one? A used MAF is usually a good bet, but it's still possible you got a bad one. When the car is idling, if you jiggle the connector, does the idle change? If so, you probably need to clean the connector and bend the pins a little bit so it gets a tighter connection. If no change, then it could be the MAF itself.

Also, no word on fuel pump replacement. If the fuel pump is noisy you definitely want to change that first and foremost. I've seen some weird things happen with a bad fuel pump, so if there's no confirmation on it being replaced I'd replace that FIRST.

Usually EGR valves don't get stuck open, the passage between the EGR valve and the plenum gets coked up so the EGR won't work.. All you have to do is lift up on the EGR valve and see if the engine stalls. If it does, then you know you're getting some flow through the EGR.

"iffy advice"? You repeated a lot of what I suggested-

[N/A Q45]

The egr is not a very probable cause but it is still worth checking. Just because something does not "usually" malfunction doesn't mean to overlook it.

[black g50]

Yesterday was pretty hot out,made a 30 mile trip and decided to feel gas tank. It was very warm to the touch even being half filled. But was interesting was the metal lines coming out of it were super hot! Couldn't keep a finger on one more than a few seconds.I wonder if this is part of the puzzle?

[N/A Q45]

Yesterday was pretty hot out,made a 30 mile trip and decided to feel gas tank. It was very warm to the touch even being half filled. But was interesting was the metal lines coming out of it were super hot! Couldn't keep a finger on one more than a few seconds.I wonder if this is part of the puzzle?

As the fuel circulates through the system it gets hot from the heat in the engine bay.

[black g50]

Any news?

[pilot_456]

Well the car was just towed to my house like and hour ago. The car will idle longer without the maf connected but it will still stall. I checked the pins on the maf like Wes said and the maf is definetly brand new. I'm about to check the other things that N/A suggested.

[goody90q45]

Is the check engine light on?
Listening from the trunk is the fuel pump buzzing like a swarm of bees?

You haven't mentioned the CEL being on and haven't responded to Wes' suggestion about the fuel pump being the culprit so I'll take a wild guess and suggest that the fuel pump controller (FPCU) has a bad solder joint that doesn't act act up until the circuit gets hot. The FPCU is mounted under the rear deck on the passenger side above the fuel tank. You can get to it easily through the trunk. Try unplugging the connector and run a jumper from the pin shown in the pic to ground. (When you unplug the connector is there any scorching on the FPCU pins?) If the engine runs without stalling the FPCU is bad. If it doesn't start you could have a bad fuel pump. The FPCU can be repaired by opening it up and resoldering the connections in the ground circuit. Let us know what you find.

[N/A Q45]

Well the car was just towed to my house like and hour ago. The car will idle longer without the maf connected but it will still stall. I checked the pins on the maf like Wes said and the maf is definetly brand new. I'm about to check the other things that N/A suggested.

I think what wes ment was the connector the plugs onto the maf. I know sometimes the metal clips in them get loose and/or corroded.

[black g50]

Think it could be IAC related after all.Noticed tach needle( slightly) going up and down in park coming home from work.

[black g50]

Update?

[black g50]

Did you ever get it looked at?

[black g50]