89 tbi idle issues

[dallred]

Just got an 89 blazer 350tbi. It will start right up and idle at first. Then when I put it in gear the idle drops. When I push on the gas it goes and runs well up through the rpms. Then when I come to a stop the idle drops and it sometimes dies. Driving on the highway is great. Around town really sucks. It also runs really rough just off idle but quarter throttle on up is great. The previous owner says the throttle body was just redone.
Any ideas or help would be greatly appreciated
Dave

[OrangeAnimal]

It could be many things. Common would be the IAC or the TPS. Possibly low fuel pressure too but since you say beyond 1/4 throttle it runs good and gets to speed fine. You can test them to be sure. I would start there. Other causes are vacuum leaks improper ignition timing and in some cases just needing a tune up.

Is the service engine soon light on?

[dallred]

No "service engine soon light" is on right now.
I will check those things this weekend.
Thanks

[dallred]

Could it be an air leak in the throttle body? How would I check that?

[OrangeAnimal]

Carb cleaner. Make sure you have the air cleaner on while doing it. Spray around the intake and vacuum lines as well as the throttle shaft. Listen for the engine to gain a few rpms while you are doing it. Use small amounts at a time otherwise you could just end up filling the air with the vapor and if it goes thru the air cleaner into the engine the rpm's will climb too.

I guess I should mention the engine needs to be running while you do this. LOL. Also be aware carb cleaner and similar stuff is extremely flammable. If you have even the smallest spark it will ignite so make absolutely sure you don't have any messed up plug wires arc or similar stuff.

[dallred]

Thanks
I understand I'm not supposed to use carb cleaner on the iac.... What should I use to clean it? Or should I replace it. Also what should I use to clean the hole the iac goes in.

[dallred]

I cleaned the iac and checked for vacuum leaks (didn't find any leaks) iac was dirty and had play in the shaft.
It us idling better... Not where I would like it. Should I replace the iac.

[dallred]

I changed out the iac. Runs quite a bit better. Still has one trouble idling. What would be the next step?

[walkerscott]

try this


http://www.thirdgen.org/tpimod2

its possible that your TPs is bad but unless you can determine its voltage at idle and full range voltage your just guessing to replace

[dallred]

Voltage on tps is right on the money....
Ideas?

[walkerscott]

what was you voltage at idle and then at Wide open throttle

Does your truck have AC
if so turn on the AC
Does the idle speed pickup? If not lets try resetting IAC

Idle Air Control tools needed

1.Torx bit # T-20 not needed if TBi idle screw is factory sealed

2.Paper Clip
How to perform a IAC reset

remove air cleaner
determine if the plug blocking the idle screw on your TBI is still in place or has it been removed

step 1 for inplace plug
step 2 for removed plug




Step 1
Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' pins.

Turn on the ignition, but don't start the engine. Wait a few seconds 5-10. Now, go and unplug connector from the IAC. (best if air cleaner is removed prior)

turn off key plug the iac back together start vehicle
test AC see if idle increases


Step 2
ONLY change this if the idle screw has been tampered with

Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, Leave it alone.
If not then Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.

Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive.


we can check injectors later if this does not work

Do you have a timing light ?

or next
potential fuel line leak between pump and pickup tube

[dallred]

The Voltage was .56 at idle and 4 at WOT.
I have AC... is inoperable.... It appears that the "idle screw" has not been tampered with. I will try the reset and see if that works.
When I start the truck up cold it runs great. After it warms up it starts to dip down below idle. It will regain idle speed. For example.... If I am driving and come to a stop light, when I slow down the idle will drop... once I am at the light the idle will slowly regain back to normal. (This is today)

[dallred]

I did the reset. It died a bunch at first then ran a bit more smooth. Still idling really low. I will round up a timing light and check that next.

[OrangeAnimal]

What RPM is it idling? It should be pretty slow. Mine is about 600rpm as per the factory tach, also just in case, the first mark on the Tach is 500 rpm's every tick mark is 100 rpm. It's not 100% accurate either. My actual speed is about 650rpm.

Oh and another note if you disconnected the battery at any point during all this you will need to drive it a day or so for it to relearn. During the first couple startups you will notice it hunting the idle speed and sometimes just depending on the truck and the weather etc. It may almost die especially the first time you restart it after disconnecting the battery. I usually give it a day or so of driving to settle in. Just depends on how much you start and stop the engine and several other factors.

[dallred]

Out of curiosity I unpluged the vacuum from the map sensor. The idle instantly went up to what sounds like normal......
Ideas?

[chevy88]

I had the same problems , as quitting at stop lights with the brake on in gear and it turned out to be a spark plug wire that was not letting spark to spark plug, i found it by accident just lucky.
Posted via Mobile Device

[dallred]

I checked the timing warm and cold today. When it just starts up cold it runs fine. The timing was clear to the edge of the timing mark at 12. Once it warmed up the idle starts jumping around. The timing jumps between 4 and 10 on the timing mark. I checked the TPS voltage again. It is .56 at idle and 3.93 at WOT. I reset the IAC again and now it doesn't idle at all. It just dies....
PLEASE HELP!!!!

David
ps. 89 Blazer for Sale.

[OrangeAnimal]

Sounds like the timing chain has stretched but you need to do as couple of easy tests cause it could also be bad plug wires.

First thing is first. Timing let's set it as close to right as we can. You need to disconnect the computer bypass connector before you can set the timing. If you did not then the 12 degrees you were seeing is about right at idle.

Dies at now after resetting the IAC do this. Disconnect the battery let it set for a couple minutes while your waiting check the connector for it the pins inside and the wiring. Also the vacuum lines are worth looking at just in case you pulled one loose. If it looks good no bent pins etc then continue on. Re Connect the battery.

Now Try and start the engine hopefully now it will run. Don't worry if it stumbles a little trying to start it. If it dies try again sometimes this happens when you reset the ECM.

Now hopefully it idles ok. Next shut it down Remove the distributor cap then with some help get a wrench on the crankshaft bolt and rotate the crank clockwise it should also be moving the rotor as well. If it isn't continue on clockwise till it does. Once you reach that point slowly rotate the crank counterclockwise till the rotor moves honestly you shouldn't get very far before it's moving .

If that looks good which it probably will the last thing is to replace those spark plug wires. I would be willing to bet you have a bad set. You can try this. Put your timing light on a different wire and see if the timing still jumps around. If so try another. Don't get discouraged and also just because you may have bought them recently doesn't mean they are good. I like to use Borg Warner or Delco wires. The cheap ones from Autozone or orielly's are junk.

[dallred]

When setting the timing what wire do I disconnect? Is it one wire or entire plug?

[OrangeAnimal]

It is a single wire, It near the plastic cover on the firewall You will see that large piece of split loom covering over the wires it may already be exposed. It has a small round connector and the wire is tan if I remember correctly.
Attached is a pic of where it should be or very close to it, In the pic on the far right you can make out the small connector. Disconnect that then set timing to Zero degrees plug it back in and your set.

[OrangeAnimal]

Here is one more this is on a 87 model. Yours is going to be over to the side though instead of directly above the distributor. Cause this is the square body style truck. First year for TBI I believe

[dallred]

Found it. checked the timing. It is right on 0.
Haven't checked the timing chain yet....
I took a picture of my distributor. It doesn't look very good. it is rusty. Could it be the pick-ups in the distributor?

[dallred]

The ring on the outside of the pick ups moves... Is it supposed to?

[OrangeAnimal]

Mine does. It also looks like ****. But the truck runs fine.

[dallred]

Could it be a temp sensor? It runs great when cold. When it warms up seems like its hunting for idle...
After I reset the iac it ran good for a little while