1994 4X4 4.3L Vortec

First off welcome to all. I have used this forum many times and read some very helpful tips! Now my issue I have a 1994 Sierra 4x4 with a 4.3L vortec automatic. I just bought the truck and the first few times I drove it it ran fine. However, yesterday I got in it to go to town it started fine. I noticed it shifted a little hard nothing extreme. I didnt think much of it because it was cold. I got to where I was going and all of the sudden it started to tach at @2000 and would not idle down? I shut it down and took care of my errand and started it up and again tach at 2000rmps? I drove to church and parked it. After church it didnt want to start, took sveral attempts to start but, it finally did but again 2000rmp at idle. I started home and it acted like the trnasimission was slipping bad! It would come in and out of gear it seemed but, it would never come out of second or 3rd gear. I did get home but, when I got there the service engine light came on, here is my question. Could these 2 things be related? I have never worked on a GMC before. It seesm odd to me that these things happened at the same time. Could this be some type of sensor problem? Or did I have 2 unrelated failures happen together? Any help or suggestions would be highly appreciated!

1st thing is that the Vortec did not come out until 96 so was the TBI engine replaced with a Vortec?

A high idle can be due to a bad TPS sensor, MAP sensor, wrong fuel pressure or a vacuum leak.

The TPS sensor can also affect shifting of your trans. First thing is to get codes. If it is really a 94, then you can get codes jumpering pins A and B (see www.troublecodes.net/GM/). If it is a 96, you need a code reader to get the codes.

Post back the codes that are found.

//2000CAYukon

Agree on all except, on some vehicles '94 was the changover to the OBDI/OBDII hybrid which cannot display engine codes by simply jumping the A & B diagnistic terminals. It can only have the codes read by a hybrid code reader. If jumping the terminals doesn't flash you the codes on the dash, then you have the OBDI/OBDII hybrid ECM. Injectors are often a tell tale of this, but not a gaurantee... at least in the 350 equipped cars. TBI was OBDI and TPI was OBDII.

i had a 1993 chevy blazer with a stock 4.3 litre vortec in it. at aec there is also a 95 blazer with a stock 4.3 litre vortec. the vortec became real common in 95 becuase i have seen many with vortec engines

I guess this would be a L35 (Vin W) Vortec engine? My mistake, I know the V8s were TBI until 96 (5.0 and 5.7L) but was not aware that the 4.3 was a Vortec starting in 92.

My bad. Now that I know it is a Vortec, fuel pressure needs to be checked.

//2000CAYukon

Thanks for all the replies, The engine says Vortec on it but, I have never owned a GMC and bought this truck used about a month ago so, I guess it is possible that the engine had been replaced. Now for what I found, after looking at the injectors I discovered that the wires and the connectors were badly burnt and melted. I had an old 87 blazer on the back of the farm and I recalled replacing the connectors on that throttle body. So I went and got the connectors off of it and replaced them. The truck does not start right off, takes several tries but, it does fire and run. However, it is still idling way too high ~1800rpm. Now I did drive the truck and it shifted fine today and it runs fine once it is started and in gear. So, at this point I would have to agree that it is either a sensor or fuel delivery related. I have checked for any vaccum leaks and can not find any.

OK I was able to get the coed today here is what I got

1 flash pause 2 flashes = 12 does this indicate diagnostic mode? I did not see this code under Vin W?

Next set was as follows:

2 flashes pause 1 flash = 21
TPS voltage was above 0.8 volts for 5 seconds when engine was running and air flow was less than 15 gm /sec, or the TPS voltage was over 4.8 volts at any time.I am guessing this is the throttle Position sensor but, does this indicate it is bad?

Next set:
6 flashes pause 9 flahes = 69 chart says TCC stuck "on"

I am not sure what these codes are telling me, any guidance would be highly appreciated!

Look at this to check out the TPS http://www.autozone.com/az/cds/en_us/0900823d/80/18/b9/7a/0900823d8018b97a/repairInfoPages.htm

//2000CAYukon

2000CAYukon, Thank you for your help! The TPS did the trick! The truck runs better now than when I bought it, idles good and shifts great! Just wanted to say thank you for taking time out of your day to help!

2000CAYukon, Thank you for your help! The TPS did the trick! The truck runs better now than when I bought it, idles good and shifts great! Just wanted to say thank you for taking time out of your day to help!

You are welcome. Glad it was something easy to fix!

//2000CAYukon