Surging idle after warmup

[sofilthy]

Hey this my first post, but I've read quite a few here. I have a 97 Aurora that is acting up, where once warm it will surge at idle and hesitate from a stop then get going. when I am cruising it will move along fine, but when I let off throttle it will dip so low in rpm that it sometimes stalls, then tries to correct and surge to over 1k rpm. Also after it's ran for a bit or warm it takes a lot of cranking to start up sluggishly.

I've done a lot of of work to the car already but can't figure out what's going on. I've changed IAC, TPS, fuel pump cause the gauge wasnt working and ran out of gas a few times, both manifold o2(other 2 didn't show a code), intake manifold gaskets, I sealed the anti backfire valve cause it backfired and blew the rubber piece off, alternator, spark plugs... Maybe some other things.

It seems as though I have a vacuum leak, but after inspecting everywhere I can't seem to find anything. Manifold looked okay, I cleaned the throttle valve and that didn't seem to help. All the hoses and connections seem okay, and they are getting vacuum it seems.

I have no idea what to do anymore and I've invested lots of personal time into it and pretty frustrated.

Another note. When I got the car the person said the valve cover gaskets we're leaking and I could see there is oil on the pan and such. Could the valve covers cause the issue?

Anyways there is some background hope some one can chip in their input.

[tigger]

Have you cleaned the MAF sensor?

Does sound like a vac leak...

[sofilthy]

Another thing I was thinking is would the cat cause this if it was getting plugged?

[sofilthy]

Yes I have checked and sprayed the maf off to no effect

[tigger]

Let it warm up, then disconnect the MAF. If it smooths out, bad MAF or vacuum leak.

[RCA1186]

I'd change the fuel filter if you haven't already, running out of gas can suck up a lot of sludge. I was told that trouble starting when warm was sometimes a fuel pressure regulator problem. I'd say check your fuel pressure when it's warm either way. Only other thing I can think of is crank sensors.

[sofilthy]

Ok so I disconnected maf and same thing, idle still all over the place. How would could I go about checking fuel pressure?

Also my exhaust smells bad could I be getting too much back pressure if its clogged? It looks like I would have to drop the cat and back to weld a new one on there or clear the guts, so I would rather not deal with that.

[tigger]

Feb 1, 2019 18:36:34 GMT -6 sofilthy said:

How would could I go about checking fuel pressure?

There's a schrader valve on the fuel rail where you can hook up a fuel pressure gauge. Most parts places will rent/loan you a gauge if you don't have one, call around.

Once you get the gauge hooked up, just turn the ignition key to ON without starting the engine and take a reading. IIRC, the first gens run about 50 to 55 PSI.


And since you're already spilling gas, pull the vacuum line off of the fuel pressure regulator. If any gas leaks from there, go ahead and replace that...

[RCA1186]

If the exhaust smells like rotten eggs you could be dumping un-burned fuel into the cat which would eventually cause it to plug up.


Found this post by aurorabrain about fueling

Oct 16, 2006 13:16:11 GMT -6 aurorabrain said:

dwiall said:

What is the fuel pressure supposed to be on a 1995 olds Aurora. I hooked up a guage to the Schroeder valve and got 38 psi. I turned in the torx screw on the fuel pressure regulator until it hit 60 psi. Is this good practice or am I doing something I shouldn't? thanks

Dave A.

Your car will run very rich, and get bad gas mileage. Your DIC will say that you are getting good gas mileage. Fuel pressure should be about 49-52 optimal at key on, with engine off. Idling it will be around 40, and will go up to 50ish with the vacuum off the regulator.

GM SI: With the ignition On, and engine Off (zero vacuum), system fuel pressure at the pressure test connection should be 333-376 kPa (48-55 psi). If the pressure regulator supplies fuel pressure which is too low or too high, a driveability condition will result.

A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:

- The fuel pump check valve.

- The fuel pump flex pipe.

- The valve or valve seat within the fuel pressure regulator.

- The fuel injector(s).

Fuel pressure that drops-off during acceleration, cruise or hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or misfire. A lean condition can be diagnosed using a scan tool. If an extremely lean condition occurs, the oxygen sensor(s) will stop toggling. The oxygen sensor output voltage(s) will drop below 500 mV. Also, the fuel injector width will increase.

[97 & 99 autobahn]

check the rubber gasket between the throtle body & intake manifold it could be torn, plus there are several vac lines that could be rotten found two 90's in this area on my 97&99 that had split 

[sofilthy]

It has been snowing where I live so the rora has been parked for a bit and I am driving a different vehicle right now, but I will check that stuff out and see how it goes. Thanks for all the replies so far!

[RCA1186]

Yep the elbows on the PCV line (either end) tend to rot out and crack.

[sofilthy]

Update!

So I checked out the fuel pressure regulator and pulled the hose and saw some fuel, left it unhooked and turned key to on, and fuel was coming out. So I replaced a few days ago and seems like everything is back to normal! Smooth as butter, for now haha.

Check engine is still on for mass airflow incorrect reading. But I suspect it's because after I sealed my leaking anti backfire valve it backfired a few times and blew off my sealant. So im pretty sure I have a small vacuum leak there. Funny story, it almost lit my hood matting on fire a few times... Pretty ripped up now haha.

Again, thanks for all the info everyone, really appreciate it!