Symptom Related Diagnostic Procedures

1. If vehicle idles rough or stalls, proceed as follows:
a. Check if EGR valve receives vacuum at idle. If so, check vacuum hose routing and correct as necessary.
b. EGR valve may be stuck open or not closing fully. Remove valve and inspect for proper closing and seating of valve components, cleaning or replacing valve as necessary.
c. EGR valve gasket may be blown or valve may be loose. Check valve attaching bolts for tightness and inspect gasket, tightening valve or replacing gasket as necessary.
d. On back pressure type valves, air bleed may be plugged. Check if valve holds vacuum with engine off. If so, replace valve.
2. If vehicle runs rough, surges, hesitates, or shows general poor performance at part throttle with cold engine, proceed as follows:
a. Check if EGR valve is receiving vacuum. If so, check vacuum hose routing, correcting as necessary.
b. EGR valve may be stuck open or not closing fully. Remove valve and inspect for proper closing and seating of valve components, cleaning or replacing valve as necessary.
c. EGR valve gasket may be blown or valve may be loose. Check valve attaching bolts for tightness and inspect gasket, tightening valve or replacing gasket as necessary.
d. On back pressure type valves, air bleed may be plugged. Check if valve holds vacuum with engine off. If so, replace valve.
e. TVS or PVS may be opening too early. Check TVS or PVS at outlet port to EGR for vacuum with engine cold. If there is vacuum, replace damaged switch.
3. If vehicle runs rough, surges, hesitates, or shows general poor performance at part throttle regardless of engine temperature, EGR valve may be stuck wide open. Remove EGR valve and inspect for proper freedom of movement of valve components, cleaning or replacing as necessary.
4. If engine stalls on deceleration, EGR valve may be sticking open or not closing fully. Remove valve and inspect for proper closing and seating of valve components, cleaning or replacing valve as necessary.
5. If vehicle exhibits part throttle engine detonation, proceed as follows:
a. EGR valve may be stuck closed. Check EGR valve for freedom of operation by pressing and releasing valve diaphragm to stroke valve mechanism. Clean or replace valve if not operating smoothly.
b. Leaky valve diaphragm may not be actuating valve. Check valve by applying vacuum. If valve leaks vacuum, replace valve. On back pressure type valve, block tailpipe as described under ``Valve Function Test'' for 1983---86 vehicles.
c. Vacuum to EGR valve may be restricted. Check vacuum hoses, fittings, routing, and supply for blockage.
d. EGR valve may be disconnected. Check connections and reconnect as required.
e. TVS and/or PVS may not be opening. Check TVS or PVS at outlet to EGR valve for vacuum. If there is no vacuum present at part throttle with engine at operating temperature, replace damaged switch. Ensure that vacuum supply is not restricted.
f. The load control valve may be venting. Check for vacuum at load control valve vacuum port to EGR valve. If there is no vacuum, replace load control valve.
g. EGR passages may be blocked. Check passages for restrictions or blockage.
h. On back pressure type valves, there may be insufficient exhaust back pressure. Check for exhaust leaks ahead of muffler/catalyst or for blown out muffler/catalyst. Check for blockage to EGR valve.
i. Vacuum hoses may be leaking. Check all hoses for damage or faulty connections, repairing or replacing as necessary.
6. If there is abnormally low power at wide open throttle, the load control valve may not be venting. Check for vacuum at vacuum port to EGR valve at wide open throttle or heavy load. If there is vacuum, replace load control valve.
7. If engine starts but stalls immediately when cold, proceed as follows:
a. EGR valve may be receiving vacuum with engine cold. Check vacuum hose routing, correcting as necessary.
b. EGR valve may not be closing fully. Remove valve and inspect for proper closing and seating of valve components, cleaning or replacing as necessary.
8. If engine is hard to start or will not start, proceed as follows:
a. EGR valve may be receiving vacuum with engine cold. Check vacuum hose routing, correcting as necessary.
b. EGR valve may be stuck open. Remove EGR valve and inspect for proper closing and seating of valve components, cleaning or replacing valve as necessary.
9. If vehicle exhibits poor fuel economy, it may be caused by detonation or other symptom of restricted or no EGR flow. Refer to step 5.