64chevy Posted January 10, 2012 Share Posted January 10, 2012 My 1989 Comanche SporTruck 2 WD 4.0L / automatic starts easy, runs smooth but sputters and sometimes stalls on deceleration. Any ideas would be greatly appreciated!! Link to comment Share on other sites More sharing options...
kyleag89 Posted January 10, 2012 Share Posted January 10, 2012 Clean your throttle body paying extra attention to the IAC. Also check your EGR valve sticking as this caused my 89 automatic 4.0 to stall when downshifting. Link to comment Share on other sites More sharing options...
64chevy Posted January 11, 2012 Author Share Posted January 11, 2012 We have cleaned the throttle body and have done the following: crank sensor, stator, idle air control motor, oxygen sensor, EGR solenoid (we cleaned the EGR valve), ignition wires, plugs, distributor cap and rotor and fuel filter. In addition I've replaced the muffler, heater core, blower, resistor, oil pan gasket, rear main seal, PVC assembly, vacuum harness and battery. Do you think an EGR valve can appear to work but not actually be working... Needing to be replaced? Link to comment Share on other sites More sharing options...
cruiser54 Posted January 12, 2012 Share Posted January 12, 2012 TESTING THE EGR VALVE FOR 87-90 4.0 ENGINE Valve Opening Test 1) With engine at normal operating temperature and at idle, rapidly open and close throttle. Open throttle sufficiently to obtain at least 1500 RPM. Movement should be noticed in EGR diaphragm. 2) If diaphragm does not move, probable causes are: faulty vacuum signal to EGR, defective EGR diaphragm or defective backpressure sensor diaphragm (if equipped), or leaks in vacuum lines or connections. Valve Closing Test 1) With engine at normal operating temperature and at idle, manually depress EGR valve diaphragm. RPM should immediately drop, indicating that EGR valve is not leaking and had been properly cutting off exhaust gas flow at idle. 2) If there is no change in RPM and engine is idling properly, exhaust gases are not reaching combustion chamber. Check for plugged passage between EGR valve and intake manifold. 3) If engine idles poorly and RPM is not greatly affected by manually moving diaphragm up, EGR valve is not closing off exhaust gas flow. Check for carbon between pintle, leaking EGR valve gasket or bad EGR valve. *************** Link to comment Share on other sites More sharing options...
64chevy Posted January 22, 2012 Author Share Posted January 22, 2012 It was a bad EGR valve. Thank you for the help! Link to comment Share on other sites More sharing options...
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