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Discussion Starter · #1 ·
Hello! I have a 1998 Pontiac Grand Prix GTP with the 3.8L S/C engine. I have ~70K miles on the car. In July 2017, the check engine light came on, and the car started bucking like a bronco. Codes were P0102, P0171, and P1404. Local garage replaced the MAF (mass air flow sensor) with a DELPHI AF10125 (OEM part). Car seemed to be fine, but then months later, I noticed that I was hitting the rev limiter when accelerating "briskly" (read: pedal down) onto the freeway, etc. I've been living with it, but now the check engine light is back on, and I am reading P0102 and P1404 codes. The light goes off after a few start/stop driving cycles, but comes back after a few days with the same codes. Does anyone have any suggestions for me please? Should I just replace the MAF a second time? The car has around 70K miles on it now. Thanks in advance for any help!
 

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I've been looking at diagnostic code charts and from that info a lean condition mat be present. A partially stuck open EGR valve is mentioned in the charts and that 1404 code. EGR valves do get carboned up and can cause a stuck pental which can cause a lean condition

I have run across stuck EGR valves. In a pinch(the electric EGR valves are a bit spendy), I have removed these valves and washed them out with a good penetrating oil(removed carbon deposits from the PENTAL shaft)and this worked. However, I've seen those problems re-occur on some EGR valves. At that point we just replace the ERG valve. Unhooking it will just set another code. My best recommendation is to scan the PCM using a DIAGNOSTIC SCANNER and see what the EGR NUMBERS ARE UNDER DRIVING AND IDLE CONDITIONS. Using a scanner like this, one can command the EGR open and closed. You probably don't have that kind of scanner so try the cleaning procedure. OR, try another EGR VALVE and see what happens. If you decide to get a new EGR, get one from DELPHI. There parts are TOP shelf.

One last bit of info, when the egr sticks, it can cause a lean condition and trigger The 171 code. Guess that's about all I have right now. Try this stuff and get back when you can..... Good luck, Jake
 

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Discussion Starter · #3 ·
Thanks for the reply. Unfortunately, I do not have a diagnostic scanner to test the EGR valve with.

Any idea if a stuck EGR valve will cause the car to hit the rev limiter as described?

Replacing the EGR does not look that hard (assuming I can unscrew 20 year old bolts).

Do we think the new MAF is working properly? What is your confidence level that replacing the EGR will work to solve the problem?

Thanks!
 

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That's a hard thing to say with out some diagnostic scanning. That p1404 code does specificly mention the EGR valve as not opening/closing correctly. Without doing a diagnostic scan to see the opening and closing of the EGR, it's just a guess.

This type of discussion has been challenging for me because I'm a auto tech and use diagnostic scanning to track down these type of problems. I/we can see specific values of opening and closing via commands from our diag scanners. Anything other than concrete data for support for repairs is somewhat of a "guess". Wish I had better info for you..... but I would recomend finding someone who does have one of these type of scanners so you can see actual opening and closing operation of the EGR. This is about the only way to know for sure it's the real problem. Good luck, Jake
 

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Discussion Starter · #5 ·
EGR Valve Replaced

Thanks for all of your assistance.

I replaced the EGR valve today. Will advise if the check engine light comes back, as it has been off for a few days now. The new EGR did not set it off upon start (good thing, I imagine).

I'm still hitting the rev limiter when going petal to the floor while getting on the freeway. Any ideas? Related to the EGR issue? I saw another post somewhere that said I need to have the ECM re-flashed. Any thoughts? Thanks!
 

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What is the RPM at when it acts up?? Also have you made any signifant TIRE WHEEL CHANGES that can effect how the PCM DETERMINES SHIFT POINTS??
When I had my best/last PCM TUNE done, The car has never been as good as it is after a great tune! "Dyno tune motor sports". When I did mine , UPS THERE AND BACK......Done. One of the things the pcm uses for shift points is TIRE CIRCUMFERENCE. Rolling distance is also used 1 FULL EVELOUTION.

Any way, (GURU) BRIAN IS YOUR GUY. Jake
 

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Discussion Starter · #7 ·
Hello, and I apologize for the delay in posting more information.

For starters, the Check Engine light popped again shortly after installing the replacement EGR valve. Now I am getting a SOLID P0401. Any thoughts please? I assume the valve is faulty and I need to replace. Thanks.

As for the rev limiter issue, no tire or wheel changes have been made. I can't tell you the RPM when it acts up, because I am accelerating full throttle, and am looking out the window. Almost appears that the car is not shifting at the proper point (i.e. "stuck" in whatever gear I am in) which is allowing the car to hit the rev limiter and cutting off the fuel supply resulting in a jerking of the car.

THANKS TO ALL!
 

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Looking at OEM CODE CHARTS, the EGR or pipeing going to the EGR may be restricted. Saw that code descriptions in the OEM FLOW CHARTS. The OEM FLOW CHARTS shows EGR SYSTEM INSUFFICIANT FLOW. That tells me the EGR IS NOT OPENING OR CLOSING CORRECTLY OR THERE'S A RESTRICTION in the EGR piping.It is possible for the exhaust tube going to the EGR COULD BE RESTRICTED. I guess to check that you would have to remove that tube supplying exhaust to the EGR VALVE. You could remove the EGR AND PLUG THE EGR port going to the intake to see if it's restricted or start the engine and there should be vacuum there. If you fire up the engine Another problem mentioned was to check for a restriction to the MAP SENSOR. I have seen a few MAP SENSORS get pretty gunked up where it is mounted into the plenum. Also the seal on the MAP sensor can get pretty deteriated which would change the MAP SENSOR OPERATION.

I guess the bottom line here is, When the EGR VALVE IS REMOVED, can you detect intake manifold vacuum on one port and exhaust pressure on the other port. If you can, that points to an EGR VALVE PROBLEM. IF THERE'S NO EXHAUST PRESSURE, THERE'S A RESTRICTION in the exhaust pipe going to EGR..... On another note, do you hear any exhaust leaks in that area??

Good luck......Jake
 
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