Mechanics

RPM DROP OFF DURING IDLE

2001 Saturn L300

Engine Performance problem
2001 Saturn L300 6 cyl Front Wheel Drive Automatic 269000 miles

In the past couple of months, I've noticed that the engine RPMs fall off as follows: falls from 650 down to around 575-600 range, is a momentary drop after which the engine recovers (but sometimes feels like it wants to die), most often noticed when the engine is thoroughly warmed up or hot, and doesn't seem to be a problem during normal driving speeds (only happens when I'm stopped). I've replaced the plugs, checked the plug wires, replaced the air filter, cleaned the throttle body, fixed a leaky vacuum hose and inspected the others, tried gas treatment, disconnected the battery to reset the computer, checked for trouble code (none recorded), replaced the gas cap (had a one-time vent valve error code, cleared it and no repeat in 1000 miles), and checked around the gas tank for signs of leaks (none). Fuel pump and level sensor are less than 1 year old (old pump died, changed both while the tank was dropped). Don't know if it's related, but also recently have twice had trouble starting after filling the tank (engine turns over normally but doesn't catch until the second try). The second time it happened I pulled away from the gas pump to the other end of the lot and tried starting and restarting the engine several times and noticed that it didn't shut down cleanly but instead had post-ignition knock for a second. Problem cleared itself up and hasn't repeated but it's been less than 200 miles. Engine still has original sensors and attachments, except for crankshaft position sensor (which was replaced about a year ago) and the usual consumables (plugs, air filter, oil & oil filter at 3K intervals). Only real problems are a small coolant leak (oil cooler section), A/C hose is bad, and oil in the spark plug wells (on my list to fix when $$$ comes available, maybe sooner if that's the source of my problem). I rack up about 100 miles/day in city traffic and these is the only glitches I've noticed but it's got me beat! Any help would be greatly appreciated, thanks!
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Pclogan
May 24, 2009.



Well, as I was reading your testament, I automatically started leaning towards, the idle air control valve and mass airflow sensor, (possibly dirty or faulty), which could still be the problem but, as I continued reading you meantioned oil in the spark plug holes, well that could possibly indicate that oil is seeping into the combustion chanmber, either through the pistion rings, or valve seals, (probably valve seals seeing that you take care of your vehicle pretty well). So with that being said, And because this symptom can have many culprits, I would start with, say the Idle air control valve, and then the mass airflow and lets hope that clears it up.

Legitimate007
May 24, 2009.
Sorry to take so long to reply to your response from a couple of weeks ago, my son had to use the car while his was down.

I forgot to mention that my vehicle is a 2001 Saturn 6-cylinder, which doesn't really have an idle air control valve. Instead, there is a vacuum-driven system that rotates a butterfly valve to regulate the amount of air in the manifold. I pulled it and checked, found it very dirty and cleaned it up like new. Also checked the vacuum solenoid and the lines as far back as I could with a hand vacuum 'pump'. So far, the sensors and all looks OK.

But! I have noticed that when I fill the gas tank the engine sometimes has difficulty starting and has to have a little push on the gas pedal to start, after which it idles rough for a few minutes. This happens more frequently as times passes. I remember that about 2 months ago the gas station's auto-shutoff switch didn't work and I overfilled the tank. After researching the problem, I wonder if the charcoal cannister and/or purge valve didn't get damaged by the excess gas. I have also noted that when I remove the gas cap while the engine is idling I hear a bubbling sound from down in the tank, like something is blowing air into the tank. (I also get erratic idle and trouble codes thrown, but that's expected.) Can you comment, please? Thanks! Paul L.

Tiny
Pclogan
Jun 21, 2009.
Wow, are you a mechanic? Because you are dead on, sounds like the evap solenoid switch or the canister purge solenoid, which ever one this vehicle has is faulty, maybe a vacuum line came of or something, of that nature, I would think that maybe the canister was damaged, either way, every thing is located in the vacinity of the canister. I m glad that you have it at least running. See what a little dirt will do!

Legitimate007
Jun 22, 2009.
It was the canister purge valve! I started with the easy stuff first, and since this is next to the air filter under the hood, I checked it first. It was sticking and really unreliable so I ordered and installed a new one. I've put a couple of hundred miles on the vehicle and it hasn't sputtered once. I'm a little concerned that the actual canister might be damaged after all (from the gas overfill), but I'll burn that bridge when I come to it.

Thanks for your help!

Paul L.

Tiny
Pclogan
Jul 9, 2009.
Awesome