high engine idle blazer

Did you clean the IACV port and throtttle body-also look for a vacuum leak

Check idle adjustment. Check cold start valve,.

i cleaned tb and checked for leaks. lines are old though i'll probally replace some of them. to rivermike rat. i don't think ther is an idle adjustment screw on this tbi unit. i don't know what or where the cold start vavle is or how to check it. i did this monday morning i took out new iac checked it was no more than one and one eight inch from base. i put the washer on , last post it was off. turned the key to on for 10 seconds then to off. started and it idled at 1500. then i pulled the connector on that plug that screws into the manifold in front of the tbi unit. to my suprise the idle went down to 1100 rpm right where it's been for the last 4 years.should i replace this sensor (what is it) .

If I'm thinking of the right sensor, it's the manifold absolute pressure sensor. Check the voltage in this sensor. At idle, it should be lower than at higher RPMs.

that sounds easy do i unplug the connection and put the probes into the connector ?

No. Keep it connected. Probe the back of the connector.

itryed the voltage test,tihs is how i did it. the red lead from the tester to the white wire on the connector . black lead from tester to black wire on connector. the voltage was higher at raised throtle than at low. i stuck saftey pins into it to do test. the sensor has a white and black wire coming out of it. did i do these the right way ?

Yes. And it appears the sensor is working properly. I've asked a colleague for some help.

i'm going to put a new iac valve in on saturday.i'll post when i get it done .

Ok.

i put anew iac valve on and the idle is the same. i was told i should have scan tool connected to see what the problem is.could i do this and are these scan tools availible to rent?

Yes, you should be able to rent or borrow one from a parts store like Autozone or Advanced. And it should tell you what is going on.

ihave obd1 the codes are read by flashes on dash board.temp on dashboard gauge is a hair over 100. computer thinks engine is still cold and won't lower the idle rpm. what do you think of that. i put paperclip in a and b terminal under the dashboard but i got no flashing of 12. someone says the ecm is bad or the diagnostic circut is not working.is there afix for this.or should i just install anew thermastat and see if this lets the engine idle down to at least 8-900 rpm.

Thermostat doesn't have anything to do with the ECM thinking the engine is still cold. A temperature switch or sensor, on the other hand, would. If the truck has an electronic choke, that could also be defective or improperly adjusted.

thanks for reply i'm goig to look into these things .i'll leave my findings friday or saturday.i'm glad you answered because i was about to make a mess and install a new thermastat.

Be sure to catch any coolant that drips out. Letting it flow into storm drains is a serious offense in many areas.

i put in a new thermastat the temp gauge went up and got hot heat back. but it didn't lower the idle. i'll post when i try somthing else

Try adjusting the idle speed screw for the idle. Happy to hear the heater is working properly again.