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High engine idle Blazer

Tiny
4UZINDIAN
  • MEMBER
  • 1988 CHEVROLET BLAZER
  • 44,000 MILES
1988 s-10 blazer 2.8 was idling at 1100 rpm for long time. Decided to try a new iac valve. Also got a new tbi gasket. Installed them both now the idle is at 2000 rpm. Is there any thing I could check besides bringing to a shop so they can test using there equipment
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Sunday, January 1st, 2012 AT 10:11 PM

18 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Did you clean the IACV port and throtttle body-also look for a vacuum leak
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Sunday, January 1st, 2012 AT 10:32 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Check idle adjustment. Check cold start valve.
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Sunday, January 1st, 2012 AT 10:32 PM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
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).
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Monday, January 2nd, 2012 AT 3:37 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
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.
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Monday, January 2nd, 2012 AT 7:28 PM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
That sounds easy do I unplug the connection and put the probes into the connector?
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Monday, January 2nd, 2012 AT 11:34 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
No. Keep it connected. Probe the back of the connector.
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Monday, January 2nd, 2012 AT 11:45 PM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
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?
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Thursday, January 5th, 2012 AT 10:43 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Yes. And it appears the sensor is working properly. I've asked a colleague for some help.
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Friday, January 6th, 2012 AT 4:48 AM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
I'm going to put a new iac valve in on saturday.I'll post when I get it done.
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Friday, January 6th, 2012 AT 11:33 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Ok.
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Saturday, January 7th, 2012 AT 12:25 AM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
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?
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Monday, January 9th, 2012 AT 10:58 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
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.
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Monday, January 9th, 2012 AT 11:03 PM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
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.
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Wednesday, January 11th, 2012 AT 1:53 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
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.
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Wednesday, January 11th, 2012 AT 7:41 PM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
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.
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Thursday, January 12th, 2012 AT 7:52 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Be sure to catch any coolant that drips out. Letting it flow into storm drains is a serious offense in many areas.
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Thursday, January 12th, 2012 AT 8:44 PM
Tiny
4UZINDIAN
  • MEMBER
  • 10 POSTS
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
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Tuesday, January 24th, 2012 AT 10:35 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Try adjusting the idle speed screw for the idle. Happy to hear the heater is working properly again.
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Wednesday, January 25th, 2012 AT 4:27 AM

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