87 Celebrity 2.8L idle surging and stalling

[EternalArianne]

I was gifted this car that sat for 5 years and was last cranked 2-3 years ago. It was originally parked because the previous owner said it would shut off after driving around for 30-45 mins and he would have to let it sit for 5-10 mins before it would crank again. It has 200,285 miles on it.

We found the fuel lines were rusted out and fuel pump was not working at all. So I replaced the fuel pump, sending unit, lines and filter. It would crank and run but was backfiring a lot and had no power. It eventually got worse and shut off when put in gear. Fuel pressure would go up to 40 PSI then drop immediately. Troubleshooting lead to leaking injector, so I replaced all six injectors and now it maintains a solid 40 PSI of fuel pressure.

Now it cranks up fine from cold and idles fine for 5-7 mins then idle starts surging (this model doesnt have a tachometer so Im not sure of the actual RPMs). Will sometimes throw code 45 (rich exhaust) but most times no code at all. If I shut it off it will not crank again without giving it gas and easing off pedal until back down to idle speed but still surging. If I unplug the IAC it will fire right up with high idle but no more surging.

Also drives/stops fine but after 5-7 mins it stalls when stopping or slowing down to turn and can hear idle surging while coasting. Have to give it gas to start again and punch it to get going because people are behind you at the stop sign. I unplugged the TCC on the transmission but it hasnt made a difference.

Ive also replaced the IAC valve, MAF sensor, PCV valve, spark plugs/wires, temperature sensor, thermostat, battery, and air filter. Also cleaned throttle body and oil change. I sprayed throttle cleaner on all vacuum lines with engine running and didnt hear any change in idle, so I assume there isnt a vacuum leak. I do not have access to a diagnostic scanner, only a basic code reader (it makes the check engine light on the dash blink out the codes). What else could be causing the surging idle and stalling?

[tlc1976]

You?ve done lots of things. The O2 sensor should be replaced at some point.

One thing I would try is bypassing the EGR valve. If that?s not working right, it can cause a huge vacuum leak. You can remove it from the intake plenum with the 3 nuts. Cut a piece of sheet metal, or even fold up several layers of aluminum foil, and reinstall the valve with the metal between. I did this on a couple of 89 2.8 a bodies with no bad effects for over 100k miles. I don?t know how long before the foil degrades so if it works then I would replace it with sheet metal soon.

Does your heater blower change from defrost to vent to floor properly? If it?s stuck on defrost no matter what, it could be a broken vacuum line going to that. I?ve had that happen before.

The vapor canister solenoid could be leaking too. One thing I do rather than spraying lines, is buy a packet of hose caps and disconnect and plug off lines. That way you can isolate sections or components.

[EternalArianne]

I actually just went and bought the O2 sensor after researching a bit more. Just waiting on my neighbor to get back with the socket to remove it, as it won?t budge with a regular wrench.

I have a feeling it?s the O2 sensor since if I unplug it and crank it from cold, it?s surging right away

[tlc1976]

What I?ve done is run the engine just enough to get the manifold hot, then it will have expanded and might come out easier. But yes in any case a socket and breaker bar can be easier.

[EternalArianne]

Ok we got the O2 sensor swapped out, still surging once it gets warm. Still throwing code 45 rich exhaust intermittently. I pressed on the EGR diaphragm and it makes the engine idle way down like it?s going to shut off but goes back to surging if I let it go. Does that mean anything as far as the EGR being good/bad?

[Pontiac6ksteawd]

87 would have a MAF sensor. Look at the strut towers, and the radiator core support, and see if you see a sticker about the speed density software being installed. If no sticker, that means it still relies on the MAF sensor, would could be faulty. Also check the fuel pressure regulator. Known to leak, and cause fuel issues. Leaking leads to fire, which happened to me on my old 87 Pontiac 6000 2.8. Another item to check would be the Idle Air Controller (IAC). Both are really simple parts to replace, although the MAF can be relatively expensive.

[EternalArianne]

I don?t have a speed density sticker that I can find. I?ve replaced the MAF and IAC (twice since the first IAC was cheap and literally came apart). If I unplug the vacuum hose from the FPR it doesn?t leak fuel so I assume it?s good.

[tlc1976]

EGR could have crud buildup and not be closing all the way even when it seats down. Or pintle could be stuck or filter could be plugged. Easiest way to rule it out is try blocking it off like I described.

Brake booster could be leaking too. Do you get couple pumps of the brake after the car is off before the pedal stiffens?

And the vacuum tank could be leaking too. It looks like a plastic blimp behind the front Of the splash shield passenger side. Access from under the car.

[EternalArianne]

Ok blocking off the EGR valve didn?t affect the idle, it just made the code 45 rich exhaust stay on all the time. I also tried the opposite blocking off the vacuum line going to the EGR to hold it open, still same. So I guess the EGR is good.

I also blocked off the vacuum line to the MAP, still same.

I unplugged the MAF just to see and it seems to make it a little better, it doesn?t surge all the time, just intermittently. If I put it in gear, it stalls. I swapped back in the original MAF and it didn?t make a difference.

The only time it will fire up and run without fail is if the IAC is unplugged, but it idles super high and seems like it?s going higher as time passes until I shut it off (scared). But I?ve already replaced the IAC (twice).

[EternalArianne]

For now Ive adjusted the throttle screw until it just barely keeps it going with only very slight surging (your hafta be really listening to hear it). It runs good now, as well as will start again without giving gas. Check engine still comes on occasionally for code 45 but this should serve my purposes as a utility vehicle until I can get the diagnostics done.

[shbiggs123]

I have an 88 Pontiac 6000 LE 2.8 that had the same strange problems. Ended up replacing the Engine Control Module (ECM) and that fixed it.

[EternalArianne]

Yeah I thought about searching around junkyards for an ECM, maybe one that has the speed density upgrade

[Pontiac6ksteawd]

Thats actually quite a chore... I did it on my 87 Pontiac 6000 2.8 when my MAF died. I ended up going to the salvage yard, and getting like 15 EEPROM's with the speed density program. They are all programmed specifically to the engine and drivetrain. 3speed, 4speed, 3.33, 3.86, and a whole host of other stuff.

Out of those 15 EEPROM's, they all worked.. But only 1 was my gear ratio, engine, and whatever else, with the software.

[85_Ciera_Rebuild]

5-7 mins then idle starts surging

IAC must re-learn...on Berreta...disconnect battery for say 30 seconds, then reconnect, apply emergency brake, use chokes too, then start up, put in forward gear, and let it come up to full temperature...on Beretta, radiator's electric fan would come on...after fan shut off, turn off ignition key.

Also, does vehicle have a MAP sensor?

[EternalArianne]

I did try the relearn process that I found on here. It idled fine for 5 mins or so then started surging up and down. Sometimes way down and nearly shut off then back up. After 10 mins I shut it off then tried to crank again and it won?t without giving it gas, but it still surges. It only happens when it?s warm.

Yes it does have a MAF, I?ve replaced it with no change, I?ve got the original one back on there now and keeping a spare as they are known to fail on these I?ve heard.