# 1989 Chevy Pickup surges at idle



## shawski73 (Aug 7, 2017)

Hello! I'm new to the forum though I have looked at some other threads. My issue: my son has a 1989 chevy Silverado; 350, auto trans. It starts and dies first thing in the morning. After 2 or 3 times of that it will start surging until it reaches operating temp. Unplug the CTS runs perfect. Items replaced: TPS, IAC, Fuel pressure regulator, Fuel pump, intake gaskets (even though the engine is freshly rebuilt), CTS, EGR valve and fuel filter. Spark plugs are new too. Checked for vacuum leaks and found none. Blocked off vacuum to brake booster to eliminate leak in diaphragm. History of the truck: previous owner overheated and cracked heads. I bought truck. New heads, pistons, rings, crank, main and rod bearings. Trans goes out after about a week, so new trans. I'm at a loss so please help. Starting to wonder about the ECM?


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## Randall Ave (Oct 29, 2014)

Replace the throttle body gasket?


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## shawski73 (Aug 7, 2017)

Randall Ave said:


> Replace the throttle body gasket?


Not yet. I have been pondering the idea though. Wouldn't that cause a vacuum leak all the time or do the metals expand sealing up after operating temp?


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## Randall Ave (Oct 29, 2014)

The throttle body bolts to the intake, if I remember correctly with three bolts. The gasket would suck in causing an erratic idle. Been a while since I've seen one of those.


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## shawski73 (Aug 7, 2017)

Randall Ave said:


> The throttle body bolts to the intake, if I remember correctly with three bolts. The gasket would suck in causing an erratic idle. Been a while since I've seen one of those.


Replaced throttle body gasket. Did not help. This is really stumping me. I've been a mechanic for 22 years and never seen this


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## secret_weapon (Jan 24, 2007)

I copied this from tech tip site that I visit for diagnostic help. I would suggest checking all grounds first. Good ground at thermostat housing? That one is for ECU.


1. Disconnect the distributor pick-up coil connector from the ignition module.

2. Verify the AC voltage output from the pickup coil is over 700 mV at a FAST cranking speed.

3. If not, replace the pick-up coil and install a NEW distributor shaft.

4. If the distributor tests OK, check all ECM powers and grounds.


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