Hello i have a question about a 91 sc 1.9 DOHC automatic
My son and i are in the process of working on his car,we bought it knowing it had a bad tranny.we have resolved the tranny problem(i hope)but it also has a rough idle and feels as it wants to die on stopping and only runs rough when in gear idles good in park or nuetral..there are no codes at all..ive cleaned the t/b spotless and no change egr valve cleaned and working....had it in the shop saturn dealer(for the tranny) they said it had a bad valve in 1 cylinder(low compression)..if the case wouldnt it idle the same in all gears? just thought id ask before i jumped into and purchased a new head..is there anything i can do for this other then that..or does it sound like that is the problem
thanks

 

Investing in a compression gauge will tell you if a cylinder is faulty from worn rings or a burned valve. If a gasket is blown there will be evidence of either oil in the coolant or coolant in the oil. Test all the cylinders for a general comparison.


Have you checked for the original engine coolant temperature sensor cracking and normally leaving a high idle rich running condition? It also fails leaving the engine in a lean condition at first start requiring pedal effort to keep the engine from stalling until the engine warms up. The two-wire sensor is prone to cracking and the replacement is brass for permanency. The two-wire connector also corrodes requiring replacement from a pc connector, junk yard air temperature sensor connector, or dealer's $30 part. Many coolant sensors have failed up until the 2000 year models when brass replaced the resin tipped sensors. The sensor is relatively inexpensive. The other possible problem would be the idle air control valve sticking, mounted below the throttle body and requiring removing to clean properly with electrical contact cleaner.


The iacv adjusts the idle speed all the time and if sticking will allow uneven engine running. Since precision stepper motors are used to finely tune the idle the valve won't move smoothly but may feel like its geared. As old as your car is it may help to clean it and try it as is before troubleshooting a possible failure in one of the two stepper motors.

 

thanks for the replay ducky i do remember the mech saying it was a burned valve ...I did replace the ECTS with a new brass one there was already a brass one in but i put the new one in anyway..


i will poke around at the other things you spoke of and see how it goes thanks again