Throttle Adjustment

I have a 1990 plymouth voyager van with a 3.0 engine. Last month I had the engine replaced with a Jasper remanufactured one by one of thier certified mechanics. As I was driving home I noticed what seemed to be a misfire, but only occasionly, and at different speeds. I checked the timing and the new wires, and they were OK. After driving a day or two and still having the same problem I realized that the misfire was actually the engine downshifting suddenly at all speeds. It was realy noticeable over 45mph. It would only happen sometimes, and for maybe one or two times. I called the origional mechanic, and he told me that the throttle linkage might need to be adjusted as it affected the shifting time in the transmission. Since he was some distance from me I took the van to a local transmission shop who had rebuilt the transmission last summer, and asked them to check the linkage and fluid level. This problem did not happen prior to the new engine being installed. They test drove the van, and adjusted the linkage and added some fluid. It now shifts better, 1ST to 2ND at about 10mph rather than 25mph, but still had the problem sometimes. I took it back to the transmission shop, and they told me the adjustments were correct and the problem was in the engine not the transmission. The engine is still under warranty, but I am not sure who to take it to. I have worked on my own vehicles fot many years, and would be able to fix this myself if all it is was an adjustment. Any help would be appreciated. Thank you.

I was wondering something. Was the manifold and throttle body from the old engine used or did the Jasper engine come with the throttle body and manifold already installed? I suspect you could have a problem with an intermittant Throttle Position Sensor or its wiring. If this checks out okey, the problem is going to be input signels to the Engine Management Computer either a bad sensor, corroded connector, or bad wiring from the sensors to the comuter. I am assuming that the CEL is not or has not lit. The computer is getting signels that indicate that you have gone to high power output when you haven’t. If you could get freeze frame data from the computer before and after the problem occurs, you might be able to spot what parameter is going haywire.

Let us know how you solve this problem. TNX

Good luck on this.

According to the Autozone on-line manual the A604 transaxle introduced in 1989 has a procedure that has to be done each time the battery is disconnect to retrain the transmission control module. The same page also has the adjustment procedure for cable controlled transmissions.

Ed B.

The manifold and throttle body were from my origional engine. I have slightly moved the stop adjustment swivel to have the transmission shifting at slower speeds, and that seems to have reduced this problem somewhat. when it suddenly downshifts it it is around 45mph going from 3rd to 2nd then back into 3rd. This evening I will adjust the lock screw per the Autozone method. I will also check the sensors wirs to see if they might have gotten pinched when the engine was installed. Thank You

Please excuse my mistake. I assumed you had the A604 overdrive transmission. If you have the three speed automatic transmission, it is not electronically controlled so my comments about computer control have misled you. In your case the transmission shifting is controlled by the throttle valve linkage and governor. So you may have to have the transmission looked at by a transmission specialist addressing the TV linkage adjustment and possible governor or valve body problems. In this case the valve body spools are thinking you want kickdown when you are just cruising.

Again keep us appraised of the outcome. We do learn from our mistakes. TNX

I’m sorry for not identifying that I have the three speed transmission rather than the A604. Last evening I again adjusted the tv linkage, and removed the cruse control linkage from the throttle to eleminate any possibility that the cruse control might be affecting the downshifting. I, also, repositioned the return spring from the tv linkage to get a little more force on the linkage. This did not seem to change anything. I spoke with the transmission shop, and will be taking the van to them after May 10TH so they can have it for a few days to road test. Thanks Again.