Light acceleration "stumble"

[g88s]

My 2002 SLS "stumbles" under light acceleration between 1500-1800 rpm.

Hve cleaned injecters, added new fuel and air filters, changed axels, changed shift body in transmission, replaced wire to cam sensor for injectors, dealer says no codes, injectors and plug and firing pattern looks normal. Any ideas?

Gary Gates

ps Dealer says moter mounts ok!

[TDK]

g88s,

Hopefully you did not replace the axles and shift body for this problem!

How about the following:

Plug wire routing (in particular after fuel rail change).

Throttle plate sticking (clean it inside).

An EGR (Exhaust Gas Recirculation) valve problem?

A FPR (Fuel Pressure Regulator) problem?

A fuel pump or fuel filter problem?

Disconnect the battery for five minutes and hope the PCM or whatever wayward electron in the system buss purges itself?

Did anything else happen (repairs, other incident) when this stumble problem occurred?

How long has it been a problem?

Does it ever subside for a while?

Is it repeatable under both cold/warm operation?

Good Luck

[KHE]

How many miles are on the car? You might want to pull the plugs and inspect them. Some of the platinum pads may be missing which may be causing the problem.

I had the same set of symptoms with my '96 Seville last fall and upon inspection of the plugs, I discovered that 4 of the 8 plugs were missing the platinum pad on the ground electrode. A new set of Delco dual platinum plugs eliminated the symptoms.

[PAUL T]

I had the same problem and it turned out to be a bad coil. Never any related codes except for the map sensor that was not bad. I would also check the plugs and wires.

[rollingthunder1994]

I have the same problem with my car. It only happens when i start the car up put it in drive and step on the gas lightly. After that it's okay. With in the last six months i changed the plugs, wires, gas filter, the the intake is clean. I have been constantly getting the PO36 EGR Pintle neddle sticking. I cleaned it several times and it still gets dirty. I guess i have to change it.

One thing i did find out though. I probably caused that problem myself because of the oil i was using. I'm one of those street racers from back in the day. So because this engine is a work horse and it does get hot, i've been using 20w50 oil and Lucus oil stabilizer in the engine for the summer. My neighbor is a mechanic at caddy and he told me that i will kill the engine if i continue using the thick oil, because it was building up carbon in the engine because of the thickness. Hey this is my first N* and i thought the thicker oil would be better in the heat. Now all i use is 10w30 but the damage is already done to the EGR.

[JimD]

....

dealer says no codes, injectors and plug and firing pattern looks normal. Any ideas?

Gary Gates

ps Dealer says moter mounts ok!

Was the plug firing pattern analyzed in the shop, or during a test drive that would duplicate your condition?

I would want to eliminate the possibility of an ignition coil that might be breaking down during certain conditions. Been there, done that one.

[PAUL T]

I have the same problem with my car. It only happens when i start the car up put it in drive and step on the gas lightly. After that it's okay. With in the last six months i changed the plugs, wires, gas filter, the the intake is clean. I have been constantly getting the PO36 EGR Pintle neddle sticking. I cleaned it several times and it still gets dirty. I guess i have to change it.

One thing i did find out though. I probably caused that problem myself because of the oil i was using. I'm one of those street racers from back in the day. So because this engine is a work horse and it does get hot, i've been using 20w50 oil and Lucus oil stabilizer in the engine for the summer. My neighbor is a mechanic at caddy and he told me that i will kill the engine if i continue using the thick oil, because it was building up carbon in the engine because of the thickness. Hey this is my first N* and i thought the thicker oil would be better in the heat. Now all i use is 10w30 but the damage is already done to the EGR.

Rollingthunder1994 have you cleaned the phenolic plates (plastic more or less) between the intake and the heads? Pay special attention to clean the mouse holes. Have you rodded out the EGR passages from the intake? All these things are pretty easy to do if you have not already did it, they can really carbon up fast.

My coil took about 6 months to finally give up. You can do a power balance test to see what cylinders are bad. You can only do this if the car is acting up at the time you check it though. Coils are about $45 a piece. The alternative is to buy one and keep switching them out until you find the right one.

[growe3]

The Oxygen sensor(s) may be failing. They can definitly cause the problem that you describe.

I don't have the dianostic code for your car, but someone on this forum should.

You need to watch the voltage (using the on-board diagnostics) of each sensor when the engine is warmed up. The voltage should flicker up and down, not be stable. I don't know what the voltage should be for sure, but probably 0 - 1.16 volts.

You may also need to have the Throttle Position Switch relearn its position. On your car that may be just disconnecting the battery for a few minutes, then reconneting it.

-George