I followed all the instructions on adjusting the TPS, yet I am still having rough idling problems.

I warmed up my car and removed the TPS plug and attached the coressponding wires to a volt meter. Started the car up and the volt meter read over 2 omhs so I adjusted it around to 0.9 then 1.

During a cold start it revs up to about 1500rpm but slowly drops and eventually will die unless I give it a little gas. After revving the car it stays at 1500rpm and begins to bounce from 1500-1600rpm. Once the car warms up it idles perfectly fine.

I have also checked all vacuum hoses to see if there were any leaks but couldn't find any at all.

My main concern is the problem when I start the car and the rpm drops. It's driving me nuts trying to figure out what it is.

Anyone have any more suggestions on what the problem could be?

Thanks,

Big

 

I would recomend setting your rpm via the FSM along with the TPS.

 

there is some kind of adjustment nut on the throttle body. I was having a similar condition to you (bouncing high idle). My neighbor looked at it and adjusted this 10mm nut that has a screw within it.

My car still doesn't idle perfect, but it isnt pulsating anymore.


He told me never to touch it. Anyone know what it is?

 

The 10mm nut with the screw within it adjusts the throttle butterfly valve opening. Adjust it at your own risk. Before you go playing with it, mark where it was originally, so you can reset it when you totally screw up your idle.

Like Wankler said, adjust your idle speed after you are sure the TPS is set correctly. Your car is an S4, so here's what you do. Take the car out for a 15-20 minute spirited drive. Make sure the engine is fully warmed up. Now, if you're sure the TPS setting is OK then go on to the idle speed.

Short the initial set connector. It's a green 2 pin female connector located in front of the driver's side strut tower. Just insert a piece of wire in each hole to short circuit the connector. Crank the engine and adjust the idle speed by turning the adjust screw on top of the throttle body. Set the idle to 750 +- 50 RPM. Turn the car off, remove the short wire and you should be set.

 

you may still have a vacuum leak. also note that the FSM has a very specific procedure for setting the adjuster screws on the throttle body

 

sorry if there was any confusion, I actually meant volt instead of omhs in my original post.

I guess I should never rule out a vacuum leak, I'll probably check again this evening, I'm pretty positive my TPS is set correctly.

Also does anyone have extensive knowledge on how air bypass solenoid valve works and if it could cause problems that relates to dropping idles during cold startups?

 

As your're driving around does your idle still bounce at stoplight after stoplight or do you notice that the bouncing idle eventually subsides as you continue to drive your car and the engine fully warms up.

 

After the car is fully warmed up, it idles perfectly at 900rpm and does not bounce. The idle only bounces during coldstart warmups, so usually when the engine has cooled down completely. Right when I start the car I give it a little gas and the rpm stays at 1500, then after a few seconds the idle will start bouncing, after a couple minutes of letting it warm up it stops and the rpm begins to slowly decrease until it stops at 900 rpm once the car is fully warm.

 

since the problem persists only upon startup I'm wondering if it has anything to do with the BAC valve or the air bypass solenoid valve? I've looked at the fsm and I guess it wouldn't hurt to check if they are working properly, but just wondering if anyone have any input on if they could cause my problem?

 

I've just about glanced through the entire manual and read chapter 4 several times and saw no mention of this screw. Perhaps, I overlooked it just as I did the actual screw.