1997 Buick Lesabre custom, 146k. No previous issues or CEL before this. My fuel level sensor was starting to act weird and i noticed throughout the months that I didn't have as much power as i used to when passing cars so I decided to change the fuel pump. It was an OEM pump at 24yrs old so it made sense. I dropped the tank and replaced with a new delphi fuel sending unit w/fuel level sensor (HP10269) ohms same as original. And I replaced OEM fuel pump with new ACDelco pump (EP339) and ACDelco strainer (TS1015) Also replaced fuel pressure sensor on tank with ACDelco (16238399). Replaced fuel filler hose and fuel vent hose brand new. Disconnected battery throughout, when i was done with the job i started it up, confirmed fuel level sensor working and it started idling around 2500rpm, (before it idled at around 850rpm) it stayed there for about 3 minutes and never leveled off. I turned off the car and restarted it, it was at operating temperature and it was idling at 1500rpm. I drove it around for about 40 minutes accelerating and decelerating in town and on the freeway. It just wants to stay at 1500rpm constantly, it was hard to stop at stop signs because it kept pulling and pulling. at one point, it looked like it was fixing itself and the rpms were staying at about 900rpm in town which is ok but once i pulled over and put it in park, it went right back up to 1500rpm and started pulling again. I can't figure it out because to me, I just replaced the fuel pump and never touched anything in the engine bay so i don't know what could have changed! It was a clean job, confirmed all 3 harness plugged in, all fuel lines good, fuel filter only 8 months old, then to top it off, i decided to scan the engine today, no CEL by the way and i got a pending P1406 EGR Valve Pintle Position Circuit. Did changing the fuel pump mess up the EGR Valve??? like I said absolutely NO drivability issues what so ever before this. Any help is much appreciated, thanks!
I did some research on this, it's not a very common problem but it does happen.
EGR valves can become stuck open or closed due to a build-up of soot particles, carbon deposits and dirt from fuel. Freeway driving conditions are the best way to help your EGR valve as longer, faster journeys allow the engine to get hot enough to get rid of carbon deposits. Did you make sure everything was nice and tight when you put everything back together? And nothing was blocking or able to leak from the fuel pump? The valve of the EGR may not open properly because of a blockage or leak in the vacuum hoses. A faulty EGR can cause an engine to idle roughly. Something else you could try is to take the air intake tube apart and clean the MAF sensor, but be careful not to break it. you will only be able to get to the outboard side of the throttle body unless you feel like taking it completely off which I don't suggest. Spray the crap out of it if there's any gunk in there, making sure you get both sides of the throttle plate, also take a rag and twist it in as far as possible to get it as clean as possible. It also could be a IAC issue, The reason the speed becomes more consistent when you barely touch the accelerator pedal is that the throttle valve will then be controlling the air which enters the motor rather than the IAC circuit. That would certainly point to a clogged and/or malfunctioning IAC situation. At idle, the main throttle valve is fully closed, unlike in a carburetor where the idle valves are partially open at idle. When the EGR valve is not properly closing at idle, it can cause a fast idle situation, which the IAC will also try to control. But it should usually be a uniformly high idle speed, rather than one which varies and then settles-in to a slower speed. But once you have the throttle body and all IAC passages and motor cleaned up, don't forget to continue the cleaning as if there's stuff in the throttle body, there also could be stuff in the lines which bring the air to the throttle body/IAC too.
0192700sALT, Hello, thank you for the response. Yes, I verified that everything from the fuel sending unit/fuel pump was nice and tight and properly secured. fuel filler tube and vent hose was secured tight, all harnesses were plugged all the way down and the hold down plastic inserted as well. the IAC valve was replaced last year. I replaced it with a new acdelco part just because i felt like it and never had any issue with it. I also replaced the vapor canister purge solenoid and the fuel pressure regulator last year with ac delco parts just because i got bored. I'm going for longevity here LOL. I will clean the throttle body and the MAF sensor(replaced last year too) and see if that does anything. Also I ordered a new acdelco EGR valve(2142274) that i'm installing on monday, Replaced that 2yrs ago with a Standard brand EGR valve so I guess i'm going ACDelco, see if that does anything. I will update after i do this, thanks
Tested out the new EGR Valve and cleaned the throttle body and nothing. Same idle trouble. Although looking around the internet, I happened to come across a gm 3800 discussion board with someone that had a 98 LeSabre. Described the problem they were having with their car and it was EXACTLY the same problems, 1500 idle, surges to 2500, goes back to normal after extended driving but once I turn off the car it goes back to high idle again. It was so exact, I had to make sure I didn't write the post I was reading!! So they said that cleaning the throttle body and changing the TPS throttle position sensor fixed it. I have never changed my TPS so it's worth a shot, I'll come back to update on my findings when I do it in a few days.
I'm happy to report that the problem is fixed!!! It was the Throttle position sensor that went bad. You will get no code if it goes out, only the symptoms listed above, so i would advise to change the throttle position sensor first. It's mysterious that it suddenly went out when I decided to change my fuel pump but whatever, it's on there and it's new and it works so at least it probably won't go out for the life of the car.
Now that [Solved] icon in the title is actually true.
I'm glad to hear the problem is fixed, I guess the throttle position sensor somehow went bad at the same time you changed the fuel pump for some reason.