Cadillac Seville / Cadillac Eldorado Forum Discussion, RPM's fluctuate while driving. in Past Cadillac Vehicle Discussion; RPMs will drop to 500 then immediately pick back up.spark plugs were just changed about a month ago....
Automobile(s): 2002.5 F55 STS/65500mi, 2004 Ford F150 SuperCab4x4
MD Eastern Shore - Kent Island
Re: RPM's fluctuate while driving.
Study and practice pulling trouble codes from your car's built-in code scanner system. Use the sticky post ^^^ "How to pull codes". Write down any codes found and whether each is Current or History. Return to the sticky to open the link with "obd2" in the address - that takes you to a Master Index of all P,B,C, and U codes. Decipher any codes found, write it all down and post it all here.
We assume you used AC Delco #41-987 Platinum plugs ? If not, all bets are off.
Clean throttlebody and all intake air ducting tight and leak-free from the MAF to the TB ?
For pictures and diagrams of your engine and some car parts, click my username, open the profile. 2 albums, 6 pages in the left column.
I've got a black kind of L shaped piece that fits over my air filter and connects to a hose but I noticed when I checked my air filter that piece loosely fits in the hose.it looked like at one time it was sealed in there, could that be causing the problem? The car runs fine, it doesn't shake when idling or anything. I can't even tell the RPMs are dropping just by looking at the gauge.
That's the resonator. A vacuum leak there (or anywhere before the MAF), will allow unmetered air into the engine, throw off the air/fuel mixture, and cause idle, and possibly drivability problems.
The resonator needs to be seated properly, and securely into the intake ducting. Or better yet, remove it and plug the hole. Do a search for the "butt plug mod". Getting the resonator out of the way makes several maintenance procedures much easier.