QuestionQUESTION: I have an '89 Bonneville LE, 3800 Vin C,132K miles.
For the past 2 weeks it starts fine, but the idle hunts when cold and warming up. It misses under light load. The problem clears when the engine is warm. No OBD1 codes are set. I have done the following:
New AC Delco R45LTS6 plugs
Fuel injector cleaner in tank
Cleaned TB throat/ butterfly with spray and cloth
Sprayed wires (5 yrs, 40k miles old) and coil pack (6 months old) with water to check for missfire - no change
Sprayed soapy water on vacuum fittings - no change
Grounded out EGR pintles - car ran worse.
Disconnected EGR. No change, set appropriate code.
Disconnected MAF sensor - car ran worse, set appropriate code.
Cleaned bat terminals and bat-to-engine ground
Manifold vacuum is 15-17 inches, steady (up and down 1/2 inch)
PCV valve checked - it rattles
No gas odor from fuel pressure regulator vacuum line
A few nights ago it started missing at freeway speeds when warm (new symptom). That stopped when I exited the freeway and drove more slowly on side streets.
Any advice would be greatly appreciated.
ANSWER: Hi Jim:
What style inginion coil(s) does this car have is it one beig coil for all 6 cylinders or does it have 3 individual coils? If it's the one big one they would cause all kinds of dirveability when cold from misfires to just plain no start. I know you sid it's relativly new but if it was aftermarket the skys the limit on wether it's good or not.... How about fule pressure cold and fuel quality if you have a restricted fileter or a pump that is slow to build pressure on cold starts that could be your issue... Ground wires on the stud under the ignition module were an issue on those cars as well. How about anyone messed with the idle stop screw? if that has been played with that will cause issues and give bad throttle position voltage to the engine computer. You could have one or more injectors going bad in this causing issues.. have you tried differnt brands of fuel. try a tank full of a differnt brand only 87 octane. that's really all I can tell you with out the aid of a scan tool and seeing what the sensor readings are and when the engine warms up seeing what the fuel trim rates are.. It's also possbale that his may have a vacuume leak when cold from a bad intake manifold gasket??? when it warms up it seals and the idle problem/misfire goes away.. Thatwould shoul up by looking at the idle control motor counts on a scan tool . . . . . Good luck :}
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QUESTION: Thank you for your detailed response. The ignition coil is one big coil, 4 months old. The ignition control module is 4 months old, too. I do not know my fuel pressure. The fuel filter is 4years and 32k miles old. No one has messed with the idle stop screw. The intake manifold gasket was replaced about a year ago. The manifold vacuum is steady, 15-17 inches, and I can’t find a vacuumleak. I installed a new O2 sensor; there was no change int he problem (the O2 sensor was old anyway). Could a dirty IAC cause the problem?
Will a scan tool read data on an OBD I car? No trouble codes are being set.
I appreciate your advice.
Jim
AnswerYes an idel control valve will cause an idle surge cold but not an issue when your driving down the road. if the fuel filter is that old change it! depending on the scan tool you are using some will work on obd cars but you need one that will read the data stream not just codes. a vacuum leak will show up when you look at the idle control motor data if the numer is real low like below 5 couns ther is a leak. when the engine is hot and in park with the a/c off the counts should be up around 20 counts.
