Have a 92 RS 305tbi. Have high idle speed and have checked IAC, TPS, and CTS and though they ohm or volt correctly, I still replaced. Checked for vacuum leak and found some that I am going to correct.
My real question is that with the 4 speed overdrive I have high rpm's (at 50 mph I hit about 3500 rpms), would vacuum leaks cause this to occur or am I looking at the wrong area and what would cause the high rpm's at 50 mph, hell I red line at 65. I count the shifts and it goes into OD.
Thanks for any replies.

 

No, a vac. leak would not cause extra rpm at highway speed. If you are hitting all 4 gears, and lockup for the converter, your revs should be much lower, IF the rear axle ratio has not been changes. L03 with a 700R4 trans should have a 2.73:1 gear in the rear axle from the factory....great for highway cruising. Sounds like someone may have changed yours.

TBI have a reputation for failed base gaskets, between the throttle body and intake. If that's not one of the leaks you have already identified, check it.

 

Tach is bad, go to the electronics board here and up top in the sticky's is a tach fix thread. Real easy to fix.

RBob.

 

Does the engine SOUND as if it is indeed in those high rpms?
If not, then RBob's idea is the way to go.

 

The motor is running high rpm's and have checked them with an external tach. Going to check what Dyno said since the ex bought it several years ago and I am just trying to help her. Plus it drives me crazy when I know something is wrong and I just need to try and fix it.

 

Think I will be reviewing the lock up situation. Would that throw a code if solenoid or sensor were bad?

 

No codes on a TCC solenoid failure. It sounds like something was definitely changed in the car. 3500 RPM at 50 MPH is really high, with 3.23 rears gears and an unlocked TCC, it is about 2800 RPM at 65 MPH.

This is also with a 2400 RPM stall converter.

Check the switches at the brake pedal, there is one that interrupts power to the TCC when the pedal is depressed. It may just be out of adjustment.

RBob.