Hello everyone I'm trying to figure out what's going on with my car. On Startup my car fluctuates from 250 to 1500 RPM and bounces back and forth for a couple minutes until becoming stable. It doesn't seem to be dependent upon engine temp since it happens during warm starts too. I thought it was the manifold pressure sensor but I replaced it and doesn't seem to make a difference any ideas?

 

I believe I've seen a few threads sounding similar to your issue. For example: https://www.northamericanmotoring.co...e-visited.html.

Does it do this only at start up? How about when you've been driving for a while and you're sitting at a light? When it dips down to 250 RPM's would you say the idle becomes rough? What routine maintenance items have you replaced recently?

See if this NAM thread may help - https://www.northamericanmotoring.co...e-problem.html. On the last page 2 individuals report how they fixed the issue for them.

 

Yes it's mostly on Startup although it doesn't seem like it has anything to do with cold starts does it regardless

 

First thing to check is your ignition coil tips, and wires....if corroded, clean them up, add some dielectric grease...it might fix it...inspect your wires, again...if very old , could be an issue...
Many don't find the issue...so.etimes it's a seasonal issue....
One question...is it a "lumpy" idle? With a miss or just unsteady?
You can try Turing the key to "on" wait maybe 10 seconds, then crank....post if it made a difference.

 

Yes it's more of a bounce back and forth until it finally settles out at the proper rpm

 

Spring and fall many see a funny idle....might be fuel related with temps and changes in fuels for seasonal reasons....
If it was kinda popping and lumpy, it might have been a drippy injectors, uncommon with these injectors, or if having the key on, but not starting, then it allows the pump to build fuel psi before the start....if it did help, then the fuel system is loosing it's prime, or the pump is failing....

 

I'm hesitant to blame the fuel system since under load the car preforms normally. As for the fuel injectors I had new ones installed last fall around this time ( had 550cc put In when Jan was in Philly). Could this be a crank sensor problem since it's fine driving I don't think it's the throttle body since I'm assuming it would have trouble adjusting under gas.