Mechanics

IDLE UP AND DOWN

1988 Chevrolet Blazer • 5.7L V8 4WD Automatic • 125,000 miles

The truck idles up and down in park and won't stay running in gear without using accelerator. Truck has new gas tank, fuel pump, fuel filter, idle air control valve, ignition control module, distributor, distributor cap, rotor, spark plugs, intake gasket, vacuum lines, and map sensor. The truck will run perfect in park with the map sensor unplugged. And will run in drive and reverse perfect at idle put when u accelerate it has no pick up or power. With the map unplugged. Have checked timing and firing order fuel pressure and compression. And all check good. Checked all vacuum lines rebuilt throttle body changed injectors. Still the truck will only run with map unplugged. Please help.
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Mikederouin88
April 12, 2014.




Spray choke cleaner at base of tbi unit they blow gaskets there and check for a soft line going to map sensor it may be sucking together

Hmac300
Apr 12, 2014.
Vacuum line to map is plastic, did a rebuild kit on the TBI and changed the upper intake manifold gasket. Put truck on a smoke machine today and found no leaks. Did a combustion leak test for the heck of it and everything is fine. The only old parts on this thing are the EGR and the electronic spark control module

Tiny
Mikederouin88
Apr 12, 2014.
Check to see if egr is not hung open andor clogged lines going to it. Also check evap canister valve for being open all the time it should only open above 30 mph it's the red valve or you can pull the line off and block it and see if it is better. Scan for codes also
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Hmac300
Apr 12, 2014.

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