90 Beretta GT 3.1L rough idle

[DukenukemX]

Now that I look at the log, there's still too much air going into the engine. But I still can't find that leak. Is there a sure fire way to find this leak? I'll probably remove the plenum tomorrow to hunt down this problem. The PCV is letting a lot of air in, cause the suction is so strong that the line that comes from the front valve cover is strong enough to hold a credit card. Also the hissing is very audible when I remove the oil cap. Not sure if that's normal. For the hell of it, I got another PCV from AdvanceAuto with no change.

[robertisaar]

at idle, there should be roughly no PCV flow. going off of experience with the 3100, if i pulled the PCV valve out of the valve cover(since it is on the front cover, not the rear like the 3.1) and still connected to its vacuum line, there was no idle change. i could put my finger over the end of it and it took a few seconds before i felt the slightest hint of vacuum. if i removed the vacuum line, all hell breaks loose as the engine sucks in a bunch of unrestricted air and the idle shoots up before the IAC has a chance to try and counteract it. if the valve were stuck open, it would act like that all the time as well.

i don't think you should be able to hear it at any time, even with the cap off. or at least i don't remember ever hearing it.

[DukenukemX]

Oh dear, I think I found the problem. Going by what you said robertisaar I took off the PCV from the valve cover, and started the car. Like you said, covering it with my finger didn't change the idle, and the sucking wasn't strong. On the other hand, the engine is still sucking air into the valve cover. Had to cover up the PCV hole with my thumb, while my other hand was on the tube from the front valve cover. Without the PCV, there was a strong suction.

I guess that means intake manifold gasket? God, I remember how much of a pain that was to change. I think I used Fel-Pro last time.

[robertisaar]

hmm..... so with the PCV removed and just a hole in the valve cover, still lots of air getting into the engine that way? that would imply that there is an internal vacuum leak.... air being pulled into the crankcase and then into the intake, maybe via the lower intake gasket? i would think that would pull some noticable amount of oil with it.

i think i read that you did, but did you attempt to seal both valve cover connections and the engine still generated a lot of vacuum? if so, i can't really come up with any other reason why any amount of vacuum would be created. blow-by would generate pressure in the crankcase, but nothing in any normal scenario would allow vacuum to be created if the PCV system were unhooked.

[DukenukemX]

i would think that would pull some noticable amount of oil with it.

There's some oil missing every so often, but nothing I payed much attention to.

i think i read that you did, but did you attempt to seal both valve cover connections and the engine still generated a lot of vacuum? if so, i can't really come up with any other reason why any amount of vacuum would be created. blow-by would generate pressure in the crankcase, but nothing in any normal scenario would allow vacuum to be created if the PCV system were unhooked.

So that would mean intake manifold gasket? I already have the lady from Advance Auto getting me a new Fel-Pro gasket. I'm getting ready to replace the gasket tomorrow, before it gets too cold for me to care. I must have not done a good enough job last time I did it, any advice as how I should go about it? Like should I cover everything with red gasket sealer? Should I go with Fel-Pro, or do you recommend a better brand?

[robertisaar]

when it comes to the 3.1, i have no idea. when it comes to the 3100, fel-pro perma-dry plus seems to be the popular choice. i would just go by the factory procedure, the 3.1s don't seem to have that many gasket issues.

while you're in there, i would look into replacing the oil pump drive o-ring since you have everything torn apart to make it easy, assuming it hasn't been done before. the original units will eventually fail and you'll have quite a fountain of oil coming out of it. i want to say the revised version(that doesn't fail, at least) is brown, made of silicone?

[DukenukemX]

while you're in there, i would look into replacing the oil pump drive o-ring since you have everything torn apart to make it easy, assuming it hasn't been done before. the original units will eventually fail and you'll have quite a fountain of oil coming out of it. i want to say the revised version(that doesn't fail, at least) is brown, made of silicone?

LOL, I just replaced that 2 weeks ago. When I take it apart tomorrow and I see an obvious cause to the problem, I'll take a snapshot.

[pocket-rocket]

An updated stock one is brown, but it's not silicone. I want to say viton but don't think that's right.

[DukenukemX]

The gasket wasn't bad, but I did put it in wrong long ago. I could see the gasket for cylinder #2 was not on proper and caused the vacuum in the oil. I'd have a picture of it, but I've been going crazy lately.

When I changed the gasket and started the car finally, the car runs bad. I can't figure out for the life of me why. It sounds and acts like it runs really rich. I can smell a really bad gas smell. I checked everything I did over and over again, besides removing the intake manifold again. I'll save that as a desperate measure.

So far everything has spark. I plugged in my laptop to see, and the engine reports high airflow. Much higher then before. Naturally I checked to see if the engine is sucking air through the oil casing like before, and it isn't. There is no huge vacuum coming into the valve covers. Had to use a piece of paper to check, where as before I didn't.

I also sprayed the engine with carb cleaner to find vacuum leaks, and nothing. Why please?

[robertisaar]

cause of high idle and possibly fueling problem may be that the ECM thinks the throttle is sitting at 1.6%, even though the plate is closed. the voltage at that point looks fine, so faulty TPS is striking again? or at least something is interfering with the TPS% calculation. considering how important that input is, it wouldn't surprise me.

the somewhat good news is that you have a bunch of IAC counts to maintain a ~1200RPM idle, so there doesn't seem to be a vacuum leak anymore.

ECM never attempted to go closed loop fueling for whatever reason.

MAP high and IAC DTCs got set....



ECM's needs to calculate a correct 0% TPS position before attempting anything else. whether that means replacing the ECM or the TPS or even just clearing ECM memory and getting lucky, something.

[DukenukemX]

Waiting on a new TPS and just replaced the wire harness to the TPS with no change. In the mean time I'll put back on the $6 TPS I thought was junk. Otherwise that ECM might be due for a change. Historically I've replaced that ECM many times.

[DukenukemX]

Just put in the $6 junk TPS with no change in how the engine ran. Would be strange if the ECM is gone after doing the intake manifold gasket. First thing I did was disconnect battery and left it disconnected until everything was put bad together. I'll wait until Monday for the replacement TPS until I decide what to do next.

**EDIT**
The log had the IAC disconnected. I'm giving up today, I'm starting to lose it.

[robertisaar]

interesting.... even with the IAC disconnected, idle speed most certainly did come down for at least part of the log.... as did calc'd TPS%. o2 sensor started to come back as well. MAP DTC still got set.with the IAC plugged in and a functional TPS, it may come back to normal.

[DukenukemX]

I left the battery disconnected overnight, so tomorrow I'll see how things will change. I did do a quick disconnect to the battery and replugged in the IAC, but still ran bad. I may check the TPS wires to see if they're not damaged. Had a friend help me and he decided to bungee cord a lot of the rear wiring at the back of the motor. If I don't see anything up to the firewall with a quick visual inspection, then I'll test the wires straight to the ECM. At least I think the TPS wires go straight to the ECM?

[robertisaar]

more or less. they don't go to anything in-between the sensor and the ECM anyways.