TylerSteez

iTrader: (3)

hey guys, I have a 86 trans am stock 305tpi with a rebuilt 700r4. Lately when I'm just about to come to a complete stop I feel the car shifting down causing the car to lunge forward as I slow down, once I come to a complete stop I feel the car pulling and I have to really plant my foot on the brake to keep it at a stop. If I was to take my foot off the brake the car will just idle all the way up and shift into 2nd without me even touching the gas.

I put in new tps and iac sensors and both set them correctly (tps at .56 closed and around 4.30 wot)

I have the correct speedo drive gear being shipped since I forgot to put one in my trans when I put the rebuilt in. I'm wondering if there's any correlation between this problem and the engine not knowing its speed.

Another thing I noticed is that if I go wide open throttle during a drive the problem disappears by the next stop sign. Any ideas? Thanks

Edit: some more info is that when I put in the trans I did set the TV cable correctly, also when it's pulling at a stop the idle seems to be at around 1100rpms

ex-x-fire

High idling engine makes less vacuum to operate the power brakes, sounds like a vacuum leak.

TylerSteez

iTrader: (3)

I was listening to the engine in park the other day and it idled smooth but I'll take a look, I replaced the vacuum lines but its possible one have came off, ill spray either at the intake gaskets as well to see what happens.

TylerSteez

iTrader: (3)

I can post a datalog if anyone feels like checking it out for me

mk1431

sound like vacuum leak and brake booster no getting enough vacuum

TylerSteez

iTrader: (3)

That'd really make my car downshift weird and pull like a horse when at a stop sign? Sometimes it's completely fine and I have no problems

Vader

That is probably the primary reason it is pulling at a stop. Idle should be more like 600-650 in Drive.

As advised, a vacuum leak could be the cause. If the brake booster is intact, inspect the other potential vacuum leaks such as the PCV, EGR, external lines, gasketed joints, injector O-rings, etc.

It might also be helpful to verify the TB is clean, including those IAC air passages. Verify that the throttle plates are moving freely, and that the shaft and bushings are not worn. Misaligned throttle plates can bind, causing that random high idle problem as well. Of course, the throttle cable must also have some slack to allow the plates to close fully.

TylerSteez

iTrader: (3)

The car has a brand new egr, temp switch, pcv, and vac lines. When I took the throttle body off previously I cleaned out all the passages and checked for slop in the throttle. everything seemed to be ok but I will look at the throttle cable and see if I have any slack, something is telling me that I dont. also am wondering about the injector o-rings, I've had some doubts about my injectors before.

I plan on making a home made vacuum smoker test out of a cigar and can and seeing where that gets me. thanks for the help everyone, I'll reply with my findings

TylerSteez

iTrader: (3)

Just did a smoke test, I have a lot of smoke coming out of the throttle spring where the tv cable and throttle cable hook up to, I seem to have a fair amount of slack on the throttle gear as well

TylerSteez

iTrader: (3)

starting to think I should just order a new one, summit has a 52mm one that says it fits 86 305TPI's. Its 4 mm larger than the stock throttlebody but people on thirdgen say that it wont affect anything

Vader

If there is a leak past the TB shaft, the bushing is probably worn. Any wear there can also allow misalignment and binding of the throttle plates when closing the throttle. If the plate(s) binds in the bore the throttle may not close fully, causing the high idle condition.

If the TB is worn it should be easy to verify by opening the throttle about 25% by hand, and while holding the throttle open trying to move the end of the shaft up, down, and around to detect any play. There should be none. You can also remove the intake bellows to observe the plates as you move the throttle shaft around to visually detect any motion.

A replacement TB would solve it, but so would re-bushing the existing TB. The larger TB will not hurt or help anything since it is not a practical restriction on the 305. If you do replace it, be certain to get a TB that supports an adjustable TPS, since some do not.

TylerSteez

iTrader: (3)

Gonna check for play tomorrow morning, what's involved in rebushing the current throttle body? I thought I read something about having to send it out to somebody to have it done

TylerSteez

iTrader: (3)

I do have movement in the tb shaft, also found a crack on the pcv hose. Id be willing to send it out and have it rebushed if anyone could recommend me someone to send it to, if not I'll probably order one off summit. Thanks for all the help everyone