91 q45 base won't stay running until ......

[Inflegend]

Hey all, I have a 91 q45 base, with 4 wheel steering,
91k miles I'm the 3rd owner.
Idle became erratic one day , the car would start and idle up and down between 700rpm to maybe 1300 until the car warmed up. Then idle would stay steady and I can drive off. This changed to car stalls after start in like 5 sec, and would only stay running after the temp got up to normal. Bought an obd1 computer, but reads no codes found. I changed the cam sensor, all coil packs, alternator went, so I replaced it and got a new battery. I'm stumped without a code error, my last resort is the dealer, or as I've heard them called " the stealer"
Can anyone help ? Oh and no ces light or any others are triggered.

[elwesso]

Welcome to NICO.

Do you have any record of the fuel pump being replaced? I would double check fuel pressure to ensure that the fuel pump is delivering proper fuel.. A bad fuel pump can do some weird things. You can know it's suspect if you can hear it clearly at idle (it will sound like there's a faint buzzing, almost like a bees nest, behind the back seat or inside the trunk).

Coil packs and cam sensors almost never fail on these cars, sorry you probably wasted some effort there. Most likely cause is the MAF sensor, not really a good way of testing, easiest to just get a used one (or a couple used ones) for $50-$100 each, swap it in, and see if it fixes it...

Still, check for fuel pressure because again it does make things behave weird sometimes when they start to go.

[Q451990]

to NICO Inflegend!

Ditto on what Wes said... most likely culprits are the MAF or FPCU. Once it's up and running, try lightly tapping on the shiny black box on the MAF and see if the idle fluctuates.

What service records do you have for the car? Timing chain guides should be on your short list if you're planning on keeping her for a while.

[Inflegend]

Hey thank you both, I had a mechanic check for operation of the pump but not the actual pressure. The pump was working So that's next on my list. But let me ask you both, is it the pump when it stars and dies but right before, by rapidly tapping get the gas pedal, I make it start and hold idle with about 3000 rims, and as soon as I release it dies!

[elwesso]

The fuel pump is a common enough failure item on the car that if I was even remotely considering it being an issue I'd change it, because it will be an issue sooner or later.. fuel pumps don't generally make it more than 100k miles in the Q, so at 91k if it's never been replaced you're on borrowed time regardless. You need to check fuel pressure between the fuel filter and the fuel rail to verify. Should be 44psi or more when you turn the key on, and 34 psi at idle.

The fuel pump can still turn on but not put out enough pressure.

Plus, you don't want it to fry your fuel pump controller, because a bad pump will definitely do that, and then the car will be 100% dead if that fails.

One thing that sometimes works to eliminate the MAF is to try and start the car with the MAF unplugged. You'll get a check engine light and not be able to rev the car above 3000 RPM (because it goes into safe mode), but if it starts and idles fine with the MAF unplugged then that's you're likely culprit.

Normally when MAF fail you'll get random bucking/jerking when cruising, or you'll get random stalls usually when the car is fully warmed up (but runs fine when cold). So, this is a little different than a typical MAF failure.

[Inflegend]

I don't have a history before 69k miles , that's when I purchased it, but the guides will be addressed also. I'm ordering another pump, I'll see if that solves the issue. I'll keep you posted . Thanks again

[Inflegend]

I don't have a history before 69k miles , that's when I purchased it, but the guides will be addressed also. I'm ordering another pump, I'll see if that solves the issue. I'll keep you posted . Thanks again

[Inflegend]

I started the car just now, don't hear that buzzing that was mentioned from the fuel pump, when I disconnected the M.A.F. car shuts off ! So next is the pressure test

[elwesso]

Try starting the car with the MAF unplugged and see if it starts/idles normal...

[Inflegend]

Did that it did the same thing , shut off after like 5 sec

[Inflegend]

Ok here's an update on my issue , after letting a mechanic hear what might be buzzing coming from the fuel tank area, we looked closers at the pump assembly since you can see it when you pull the carpet down, I touched the ground wire and the buzzing got louder! Turns out someone twisted another found wire and blacked taped it. So it was a loose connection at the ground causing all my headaches!

[3Q Jay]

this sounds like someone very crudely bypassed the FPCU (fuel pump controller).
your FPCU is probably smoked due to a combination of age, less than robust original design, and restricted fuel flow thru the filter.