Rough idle.

What could cause poor idle on a 97 Grand Prix 3.8L/NA? I just replaced the intake manifold gaskets (both top and bottom.) The car sputters at idle speeds and up to about 1300 rpm. Sometimes it's hesitant on acceleration because of it. After it gets going, it is fine. Check engine light codes for cylinder misfire and lean fuel levels. I've checked a couple times and I did reconnect all sensors and vaccum lines correctly. I did replace the EGV gasket which looked like it may have been leaking and a vaccum line that had a split connector, but neither helped any. This problem started after I replaced the manifold gaskets.

When did you replace your plugs and wires last?

Did you get any codes for misfire and/or lean fuel, or did you check and didn't get any? You weren't very clear on that. Like JesseP28 asked, did you change the plugs and wires while it was apart, and if so, what brand did you use? Did you get the PCV valve in and use both o-rings, the large one at the top of the housing and the smaller black one that goes around the PCV valve itself?

I didn't replace plugs or wires this time, but they aren't too old. The plugs are about 25,000 miles and the wires about 55,000 I think.

Yes, I did have codes for both misfires and lean fuel.

Actually, I did replace the PCV valve when I did this. I believe everything went back together right, but I'll check it out when I get home tonight.

was the code p0300 (random mis-fire) or p030X (x being the number of the specific cylinder missing, ex p0301 would be cyl 1, p0302 cyl 2, etc...).? If it's a spceific cylinder misfire, coupled with the lean mixture, would indicate a bad injector on that cylinder.

was the code p0300 (random mis-fire) or p030X (x being the number of the specific cylinder missing, ex p0301 would be cyl 1, p0302 cyl 2, etc...).? If it's a spceific cylinder misfire, coupled with the lean mixture, would indicate a bad injector on that cylinder.


I read and reset the codes twice. The first time it was p0300 multiple misfires only. Second time was p0302 and lean fuel on cylinder 1.

I thought about the injector, but I thought that if there was a cylinder with a bad/clogged injector, it would get worse at a higher rpm. (Because the need for more fuel at a higher rpm.) Above 1300 rpms, the problem pretty much goes away. That and the fact that the second reading showed a misfire and lean fuel on different cylinders.

I haven't noticed a difference in gas milage.

I guess it's time to recheck what codes are set now. Plus I still gotta check the PCV valve to make sure the o-rings are in there right. I didn't get to that last night.

Thanks all for your help and ideas!

I ran over to Checker and borrowed their code reader during my lunch break.

The codes that came up are:
p0171 Lean Cyl 1
p0302 Misfire Cyl 2
p1406 EGR Valve Pindle Position


Before, the first time I scanned it and got a misfire multiple the second time only cyl 2, so I thought it was a fluke, like only cyl 2 was caught or something. Now only cyl 2 and the lean fuel on cyl 1 both come up again. Maybe I have multiple problems.

Any ideas? I don't know what the 1406 code means.

I ran over to Checker and borrowed their code reader during my lunch break.

The codes that came up are:
p0171 Lean Cyl 1
p0302 Misfire Cyl 2
p1406 EGR Valve Pindle Position


Before, the first time I scanned it and got a misfire multiple the second time only cyl 2, so I thought it was a fluke, like only cyl 2 was caught or something. Now only cyl 2 and the lean fuel on cyl 1 both come up again. Maybe I have multiple problems.

Any ideas? I don't know what the 1406 code means.

In the order of priority checkout the EGR code first. The EGR valve will cause misfire and a lean trim problem. It is a valid DTC error code indicating an electrical problem between the PCM and EGR valve. The PCM monitors EGR pintle position sensor to ensure the EGR valve is responding to commands from the PCM. The PCM is not seeing a proper feedback response. Voltage is less than .14 volts at all times or greater than .4 volts when EGR is commanded to zero or the closed position.

BTW - Several things can be checked such as the PCM 5 volt reference signal, etc.

:werd: I second what Bob said.

Here are a couple of things to try that won't cost anything but a little time:

Remove EGR valve for cleaning:
Remove EGR electrical connector. Then remove two 13mm nuts holding it on the flange. Clean EGR spring loaded pintle with carb cleaner. Make sure pintle moves freely. Use WD40 spray. Also, if you remove EGR you may need a new gasket.


EGR Relearn Procedure (must have scanner):
With engine off, disconnect the electrical connector to EGR valve, take key to on, reset DTC error codes with scanner and immediately take the key to off position. Then re-connect electrical connector for EGR and take the key back to on.

Here are a couple of things to try that won't cost anything but a little time:

Remove EGR valve for cleaning:
Remove EGR electrical connector. Then remove two 13mm nuts holding it on the flange. Clean EGR spring loaded pintle with carb cleaner. Make sure pintle moves freely. Use WD40 spray. Also, if you remove EGR you may need a new gasket.


EGR Relearn Procedure (must have scanner):
With engine off, disconnect the electrical connector to EGR valve, take key to on, reset DTC error codes with scanner and immediately take the key to off position. Then re-connect electrical connector for EGR and take the key back to on.


Thanks, I'll try cleaning and lubing the EGV pintle tonight. Maybe it's just clogged or stuck.

How can I test the electrical part of it? Can I connect a volt meter to the connector to see what it is reading and what will that tell me?

Thanks, I'll try cleaning and lubing the EGV pintle tonight. Maybe it's just clogged or stuck.

How can I test the electrical part of it? Can I connect a volt meter to the connector to see what it is reading and what will that tell me?

Yes but you will need a GP wiring diagram for pins to check. Try cleaning and the relearn first. If that doesn't work we can probably provide the info needed. A lot of us have service manuals.

I just though of another possibility, perhaps.

Bob, you said in another thread here from a few days ago called Service Engine Soon - Insufficient EGR flow (http://www.automotiveforums.com/vbulletin/showthread.php?t=544236) that perhaps the EGR stovepipe in the upper intake manifold going bad could cause EGR codes.

I'm not exactly sure what the "stovepipe" is. Is it that thin tube in the UIM? There is a clip in the gasket that holds it in place.

Remember, I just had the intake manifold apart. About a month or so ago I replaced a leaky lower intake manifold gasket (that common problem.)

If that piece moved out of place when I was putting it back together, could this be causing my problems?

I just though of another possibility, perhaps.

Bob, you said in another thread here from a few days ago called Service Engine Soon - Insufficient EGR flow (http://www.automotiveforums.com/vbulletin/showthread.php?t=544236) that perhaps the EGR stovepipe in the upper intake manifold going bad could cause EGR codes.

I'm not exactly sure what the "stovepipe" is. Is it that thin tube in the UIM? There is a clip in the gasket that holds it in place.

Remember, I just had the intake manifold apart. About a month or so ago I replaced a leaky lower intake manifold gasket (that common problem.)

If that piece moved out of place when I was putting it back together, could this be causing my problems?

On the P0401 that was related to the EGR flow test where the error pops up after a PCV valve job when the black o-ring is omitted. It causes loss of engine vacuum. Any loss of engine vacuum may affect the EGR valve as far as when the PCM tests it or calls it into service. It affects Manifold Absolute Pressure (MAP).

The stovepipe is that thin tube part on the left hand side of the UIM/LIM. You can see it when the throttle body is removed at the point where the throttle body hooks up to the UIM. The gasket sealing around it is important. I would say that if it did not mate up good the outcome would be some sort of internal vacuum leak so its possible.

However, the EGR code you are getting indicates the EGR is not functioning properly mainly electrically than indicating that there is an actual EGR flow problem.

Whatever your problem is I guess we can all agree that it has something to do with the UIM/LIM job.

Here's what I did last night...

Installed new black PCV oring.
Removed EGR, cleaned and lubed the pintle. It wasn't very dirty and the pintle already seemed to be moving ok.
Checked all plug wires and vacuum lines.

Unfortunately, I don't have easy access to a code reader, so I wasn't able to reset the EGR like you said to. I don't have the money to buy one right now, so whenever I need it, I have to borrow the one from Checker. I'm going to have more time this weekend to work on it, so I think I'll wait until then and borrow it for a couple days.

What I noticed... I had the engine running while I was down there inspecting some of the vacuum lines and stuff, and I heard what sounded like an air leak, but I couldn't find it. It sounded like it was coming from under the throttle body or under the egr; at least on that side of the engine. I felt around, but I couldn't feel any air. I think I'm going to have to take the throttle body off and look at that pipe that connects the egr to the manifold. (Is that the thing that's called the stovepipe?) Is that pressurized? Is there anything else down there I should look for? Both the lines that connect to the side of the throttle body are ok.

I was also wondering about something that's inside the UIM. It's a small plastic tube. There is a clip on the gasket that holds it in place. I think I got it back where is was, but what is it for? If I didn't put in back in place right, could that be the cause?

Thanks

just a note, P0171 is system lean bank 1, not cylinder 1. This would still indicate to me that it's an injector issue on cylinder 2, where the misfire code is. Just my :2cents:

just a note, P0171 is system lean bank 1, not cylinder 1. This would still indicate to me that it's an injector issue on cylinder 2, where the misfire code is. Just my :2cents:

Thats not totally correct on the DTC error code Rich. I agree it has nothing to do with cylinder 1. The PCM does not differentiate between individual banks of fuel injectors such as Bank 1 or Bank 2. Plus you cannot go by the generic DTC error codes that may be listed with a scanner or whatever material is being referenced. DTC P0171 (Fuel Trim System Lean) is a general error code pertaining to all fuel injectors. A system lean condition has been detected causing the addition of more fuel to compensate. Bank 2 codes are not applicable to the way a PCM is programmed in a 1997 Grand Prix. The only other applicable code would be P172 which is Fuel Trim System Rich.

So, based on that DTC error code there is no way to tell conslusively which fuel injector, if any, may be causing his problem. P0302 could be fuel or ignition. Just my two cents. :2cents:

BTW - If there is any doubt refer to the 1997 GM Grand Prix Service Manual.

just a note, P0171 is system lean bank 1, not cylinder 1. This would still indicate to me that it's an injector issue on cylinder 2, where the misfire code is. Just my :2cents:

Oh, bank 1... So are cylinders 1, 3 and 5 on one bank and 2, 4 and 6 on the other, or how do they split those up exactly? That does make sense. I was mistaking it as cyl 1. I could see how some dirt and grease could get into the end of the injector as I was putting it back on the car or it could be unrelated to the manifold gasket change I did (although it started at the same time.)

Is there a way I can clean the FI by hand or would trying a good FI cleaner additive be the best idea?

Who knows, maybe the air noise I am hearing is in my head...

Oh, bank 1... So are cylinders 1, 3 and 5 on one bank and 2, 4 and 6 on the other, or how do they split those up exactly? That does make sense. I was mistaking it as cyl 1. I could see how some dirt and grease could get into the end of the injector as I was putting it back on the car or it could be unrelated to the manifold gasket change I did (although it started at the same time.)

Is there a way I can clean the FI by hand or would trying a good FI cleaner additive be the best idea?

Who knows, maybe the air noise I am hearing is in my head...

NEGATIVE. If you review my post I clarified that for you. Bank 1 is applicable to all 6 fuel injectors. There is no monitoring system dividing cylinders 1, 3, 5 and 2, 4, 6 into banks. There are no Bank 2 DTC error codes applicable to your model Grand Prix.

Whenever you do a UIM job it is possible something happened to the fuel injectors since you pull the rail with injectors off. Did you use new lower injector o-ring seals?

If you suspect a fuel injector I can post a procedure we have used which will clean all of them at one time. Or try some Lucas fuel injector cleaner added to a full tank of gas.

I was going to include the fact that our cars only have one upstream oxygen sensor (making the bank 1, bank 2 part of that generic code a moot point), but our internet connection went down ( I just got back on) as I went to edit my reply. Since he has a fuel system lean and a specific cylinder mis-fire, that makes me believe it's a faulty injector on cylinder 2 causing both codes. A bad plug or wire on cylinder 2 would usually cause a system rich condition due to the extra unburnt fuel, agree?

NEGATIVE. If you review my post I clarified that for you. Bank 1 is applicable to all 6 fuel injectors. There is no monitoring system dividing cylinders 1, 3, 5 and 2, 4, 6 into banks. There are no Bank 2 DTC eror codes applicable to your model Grand Prix.


Bob, sorry, I didn't see your post before I started mine.

I did use new o-rings on the FI's, but I could see how some greasy dirt stuff on the engine could have possibly gotten into one end of one of the injectors when I was reinstalling them... I bet that's happened to someone before.


Rich,
What you said about fuel lean/rich codes makes sense to me.


I'm going to get some of that good FI cleaner you suggested Bob. If that doesn't work, Sunday is the day I'll tear the thing apart, working backward until I find something that doesn't look right. This started when I did the manifold gasket change, so it's got to be something to do with that. Work backwards checking every part, connector, vacuum line, gasket, whatever as I go.

If it is a bad fuel injector on cyl 2, I should be able to disconnect the plug wire for cyl 2, start it, and have minimal effect as compared to disconnecting a different plug wire and running, don't you think?



(BTW, yeah I know that was 42 minutes from the time you posted until the time I posted... I opened the window and left to do some other things before I finished it lol)

I was going to include the fact that our cars only have one upstream oxygen sensor (making the bank 1, bank 2 part of that generic code a moot point), but our internet connection went down ( I just got back on) as I went to edit my reply. Since he has a fuel system lean and a specific cylinder mis-fire, that makes me believe it's a faulty injector on cylinder 2 causing both codes. A bad plug or wire on cylinder 2 would usually cause a system rich condition due to the extra unburnt fuel, agree?

Possible Rich but its hard to say. I reviewed lean and rich trim circuits and corrective action in the SM. There are at least a dozen possible causes which happen to mirror each other. To rule out the respective injector I'd run a resistance test on the coil and then NOID it. If all else fails then pull the rail and manually clean that one injector and check the o-ring out. The o-rings should be replaced and not re-used.

HI,
I spend $1700 and had the smae problems you had. Heres the fix. Use an 89% octane for your fuel. After about 2 tank fulls of gas you will notice the differance.
Al
Good luck

uh, not on this planet. 89 octane would have no effect on a specific cylinder misfire.

uh, not on this planet. 89 octane would have no effect on a specific cylinder misfire.

:werd:

I use 86 octane regular unleaded in my Regal LS with Series II 3800 and it never misses a beat (114K miles). Of course its top tier gasoline and not from Wally World. :lol:

Spend $1700 to find out its a gas problem. I don't know about that.