Dumb Question Help!!!

[clean71]

Alright this is the deal...

I go to take my truck out for a drive today and everything seems cool. Then as I'm coming up the street to my house (with my foot off the pedal), I notice that I am accelerating. I slow down and then stop, but truck wants to keep going, tires start spinning??? WTF I put the truck in neutral and it's idling fine. I put the truck in park, idle is fine, why is it wanting to take off when in gear???

Truck is a 68 chevy short step w/ 98 ls1 and 4l60e tranny. Any ideas before I take it to the shop??

p.s. I just had the tranny rebuilt, so if that's the problem, I'll take it there as it's still under warranty. I've only put about 1000 miles on it since the tranny rebuild.

Thanks in advance.

[Longhorn Man]

Does it still have the throttle rod linkage? The engine may be leaning when you gas it and binding the throttle. The old style motor mounts were known for this, there was a recall on them.
However, even if you have the newer mounts, they probably allow for more movement and lets the rod bind.

[Peregrine]

Apparently you haven't taken it out for a fast enough spin for it's tastes, it just wants to go.

[rodnok1]

Sounds like a broken motor mount on the drivers side. Your truck has a throttle rod right? The engine tries to lift up on the drivers side and will cause the throttle to jam. Usually only when in gear. I had a 68 Nova do the same thing, I run a chain on the left side of my motor to keep that from happening to me in my 64.

[clean71]

Alright, I'm a dumbass when it comes to engine stuff. However, It is a fuel injected engine and it feels fine when I have my foot on the accelerator. However, when I take my foot off the accelerator and it's in gear it'll do about 50mph w/o giving it any gas.

If it was the linkage, wouldn't the engine race in neutral or park as well?

At any rate it's not a broken motor mount, I just checked. Thanks and keep the suggestions coming.

[Longhorn Man]

Let us know what the shop finds.

[dtlilly]

Only thing I can think is torque converter hanging up. Just a guess, and don't ask me how or why, I don't know a thing about auto trannys, especially computerized 4 speeds.

[dwaite72lnghrn]

My guess would be the lockup isn't comming off when you slow down leaving the engine tied to the driveshaft. Once to put it in park or neutral it disengages. JMO

[clean71]

So it's a tranny problem then?? If that's the case, she's going back to the place that rebuilt it.

[68C15]

'98 LS1? doesnt the TR sensor tell the pcm which gear its in to then determine the idle RPM? with a scan tool you should be able to read the data to see if it is the problem.
as you can probably tell these newer fuel injected powertrains require some in-depth diagnostic equipment..
try to adjust the sensor (may have been bugered upon installation). if this doesnt help then you just may have to take it to a shop. I am at work right now so I will log off here & look up the procedure for you in an attempt to save you some $.

[68C15]

according to Mitchell the procedure for adjustment is to set it so engine will start in park or neutral only. further testing is possible but will entail a scan tool to read the data. I can fax you the test print-out if you want. send me a PM if you would like this as it would be easier for me to find than looking for this thread.
(the TR sensor-PNP switch does in fact have an affect on the idle speed & also the EGR function among other things.

[sneakysnake]

[QUOTE=clean71]

If it was the linkage, wouldn't the engine race in neutral or park as well?

At any rate it's not a broken motor mount, I just checked. QUOTE]

I had dibs on a motor mount too.
The reason it doesnt do it in park or neutral is when its in "gear" the torque twists the engine and tranny causing the throttle to accel.
curious to know the verdict.

[Longhorn Man]

I still think it'll be a binding throttle myself. (If it is still the rod)
A converter staying in lock up will stall the engine. Kinda common if you're in lock up going down the freeway and do a panic stop....the brakes bog the tranny enough to stall the engine. Done it many times.

[chevydog66]

I would say that it has to do with the electronics of the lock up convertor in the transmission. Take it back to the trans shop. Just my .02

[bagged_gmc]

sounds like you started to run out of gas!

[68LSS1]

I'm sure he's got a cable to actuate the throttle body on the LS1. It could be binding still but I'm unclear on whether it idles high in park or nuetral? If it doesn't remove the inlet tube to the throttle body and manually open the throttle body a few times to see if it's catching. Make sure it is closed when released. IF it's doing it in park and nuetral than I go along with a converter/wiring/sensor issue. One last possibilty would be a stuck IAC. What is the rpm at idle? I don't think with the IAC stuck full open would cause your problem.

[clean71]

RPM @ idle is about 900-1000. I'm beginning to wonder if it is the TPS acting up. How do I test this?

[68LSS1]

TPS sensors usually make you have a "dead" spot when they are bad. You can check them with a old analog type meter. Watch the scale as you open the throttle. Should be a nice sweep as you go open and then closed. Any jumps or fluctuations mean it's bad. It's just a variable resistor.

[franko72]

sounds like a solenoid is engaging incorrectly at your carb. due to a short circuit when you place tranny in drive.also could be a linkage interference problem between the throttle linkage and the shifter linkage.