The most common cause would be a faulty Coolant Temp Sensor or connecter. It threads into the intake manifold, left side of the thermostat housing facing the front of the engine.

 

The most common cause would be a faulty Coolant Temp Sensor or connecter. It threads into the intake manifold, left side of the thermostat housing facing the front of the engine.

I disagree with the coolant sensor. My 1990 Camaro with tbi also had this same problem. Try changing out the Throttle Position Sensor (TPS) it is located on the drivers side of the throttle body. That did the trick for me.

 

Possibly could be the TPS. The CTS has been the culprit most times for me.

Best thing to do would be check the trouble codes before you start throwing parts at it.

Good luck! Let us know what you find

 

Start with the coolant temp sensor.

If you have an ohm meter (or a multi meter set to ohms) Check the coolant temp sensor described by GMC Boogie.. I don't recall the values but I think somewhere around 10k at 70 or so degrees? Info should be available online.
If there a infinite ohms or zero ohms then its bad.. This would cause a flooding problem.

You can use the same method for the tps, hook up the ohm meter and the resistance should change as you move the throttle. You will have to look at a schematic to figure out which two to measure.

Something that recently happened to me that caused that symptom was a clogged fuel return line.. making the pressure sky rocket. I suggest checking fuel pressure as well.

That'll give you a few things to check at not cost..

Good luck! lets know how it goes! :thumbup:

 

Start with the coolant temp sensor.

If you have an ohm meter (or a multi meter set to ohms) Check the coolant temp sensor described by GMC Boogie.. I don't recall the values but I think somewhere around 10k at 70 or so degrees? Info should be available online.
If there a infinite ohms or zero ohms then its bad.. This would cause a flooding problem.

You can use the same method for the tps, hook up the ohm meter and the resistance should change as you move the throttle. You will have to look at a schematic to figure out which two to measure.

Something that recently happened to me that caused that symptom was a clogged fuel return line.. making the pressure sky rocket. I suggest checking fuel pressure as well.

That'll give you a few things to check at not cost..

Good luck! lets know how it goes! :thumbup:

I was going to get a code reader but this '89 C30 Step Van doesn't have an ODB1 port (that I can find) so the suggestions on manually testing the components really helps.

I've unfortunatley run the battery down and probably won't get to test anything today as its charging right now.

Thanks Everyone - this gives me some ammo to start with...

 

you don't need to buy a code reader. try to find the connector like the one pictured, with the key in the off position, run a paperclip from a to b and turn the key on. The service engine soon light will start flashing. Should flash code 12 first- one flash followed by two flashes. Should do that twice than flash the code that originally is the problem, the one I had last I think was a code 15 for the ect. Than it will flash code 12 again when it's done.
The aldl connector should be on the drivers side under the dash.

 

I was going to get a code reader but this '89 C30 Step Van doesn't have an ODB1 port (that I can find) so the suggestions on manually testing the components really helps.

I've unfortunatley run the battery down and probably won't get to test anything today as its charging right now.

Thanks Everyone - this gives me some ammo to start with...

OK - I found the port and got a scanner - I needed one anyway (the best excuse to buy tools) and nothing is being reported ain:

TPS checked out, as did the CTS using an ohm meter...

I pulled #1 plug and it was fouled and smelled of gas, #8 was fouled and wet with gas...so I'm heading down to get some new plugs as the old ones look really bad at the electrode anyway....

Any other cheap ideas? My only other option is to have this thing towed to a shop and I'd rather not go that route for a rig I'm trying to sell!

 

Ya know it might be a simple thing. The fact that it runs only with your foot on the throttle suggests that when it comes off the fast idle motor, the throttle opening is insufficient to feed idle air. Given that there is no fuel connection to the throttle it certainly isn't a carburetor's choke and accelerator pump that keeps it going.

This is not to say that there isn't a problem with the temp sensor or the throttle position sensor. But I'd get the manual and make sure the throttle adjustments and the fast idle motor are working and adjusted properly.

Bogie

 

Pobably the TPS

I had a 87 K-10 350 TBI that had idleing problems.

Have you ever changed the O2 sensors? If they are bad, the TPS will get a false reading.

The sensors are cheap, but with the age of your van....they won't come out with ease ain:

 

Thanks everyone I finally got it figured out and running.

The reader at first showed no codes - but I forgot the battery had run down and I had removed the cables and cleaned the terminal ends before charging - this resetting the computer - doh.

It still wouldn't start and so I started with the spark plugs. I pulled #1 and #8 both were fouled and wet with gas. I think I has read somewhere that these low compression engines have a tough time with fouled plugs.

I looked the plugs up online and neat...the truck had the completely wrong sparkplug - one made for a smaller truck .035 gap. The ones that fit the truck where a different #, shorter and had a .045 gap.

That being said, once those were replaced - the truck started right up and ran like a top...drove it around the block flogging it the whole way and thought I had the problem solved.

Got home, shut her off - wouldn't start again. ain:

So I got the reader out and it was reporting the CTS - once that was replaced (and the sparkplugs) now it starts and runs like it always should have...I should have looked at this back in Nov. 06 when I bought it - probably would have saved me 100.00 bucks in fuel alone!

Again thanks everyone for their suggestions. Now who wants to buy this thing? :thumbup: