| > >
| > > Buick Century Limited 89 3.3 300,000 km | > >
| > > Starting cold, drive at about 60kph, let go gas pedal, going for few | seconds | > > then stall. Will do this 2 to 4 times for the first 5 to 10 mins then no | > > more problems. | > >
| > > When it's stalls, I put on Neutral, restart the engine, put back on | Drive | > > and go. | > >
| > > Looks like the problem persist only when tranny's cold. The engine will | also | > > hesitate sometimes when pushing the gas pedal but only for the very | first 1 | > > or 2 seconds, then it goes back ok, but this symptom is omnipresent | whatever | > > hot or cold. | > >
| > > Also, on hiway, let's say at 100kph (speed not revelant), as soon as | there | > > is no more "pull" (fwd) needed (ie: down a hill or overpass), the tranny | > > shudder like it's "in between" two speed goin up and down very rapidly. | > >
| > > Is there any other thing to check besides changing ATF fluid? A selenoid | > > valve perhasp? | > >
| > > Any clue? | >
| > IMO, the 3.3 is one of the best engines GM/Buick ever made. | > Do the usual, clean the throttle body, clean the MAP, check the plug | > wires with them hot, fix all the vacuum leaks, clean the IAC, check the | TPS. | | Did that already. plug need to be replaced soon, will do next month, wires | are 6 month old only, TB cleaned 2 weeks ago, MAP cleaned at the same time, | Vacuum seems OK since cruise control works great, Scanner tool (Snap on) | show all sensor data as OK and within range including TPS and O2, no trouble | codes, coil packs checks out OK. | | Did I missed something?
Can you detect any odours, vapour or smoke when it stalls. If so check the throttle position sensor. That would account for your transmission's apparent gear selection fault. The TPS also sends data to the Buick's transmission control unit. When the TPS says you got her floored, your secondary fuel is active, your spark curve is shortened but your not giving it any vacuum to go with all that juice so a nasty foul smell should be there.
After that I'd look at the EGR and crankcase ventilator valves. (Bypass and Change for cheap). You might want to test the vacuum and take a long listen around your intake manifold when the engine is good and hot and turned OFF. Listen for any hissing or coolant boiling off inside the manifold. That would be an intake manifold gasket.
That would thankfully be the least likely cause. My bet is TPS or EGR. Good Luck. Let us know.