Sudden "thunk" and pause while driving...

[Steve C.]

Greetings. Trying to diagnose an issue that is this: when I'm on the highway my Previa will make a clunking noise and stall out for a brief moment. Like a loud, hard shift you might hear with an automatic transmission. This happens about every 20 minutes or so. It does not stall the van, it just happens and the van keeps going at the same momentum. A friend suggested pouring a cup of rubbing alcohol into the fuel tank when I fill up to see if it dries out any water in the bottom of the fuel tank. I'm worried its something more major. Van is a 91 manual alltrac with 212k miles. Any help appreciated.

[Steve C.]

Same the Previa master in Seattle knows the fix!

[mountainhick]

I have this too, or something much like it. My van has done this since I got it. I call it the hiccup.

I used HEET and ran a can of BG 44K, and changed fuel filter: No difference

I posted here a long while ago and Tim suggested possibly the wire going to the Throttle position sensor which can break under the insulation. Mine looks OK and the hiccup problem is same as it ever was. I would expect it to get worse if the wire is progressively getting detached.

Just out of curiosity and just to have an extra on hand I pulled an ECU from a junkyard Previa yesterday and will try it.

Seems to me it is probably something intermittent in the electrical system, ECU or some sensor, but I don't know,

It is un-nerving.

[Steve C.]

I meant Samie in my previous post (he is the Previa guru in the PNW). He has seen this many times and thinks it's the throttle body positioning sensor/butterfly something or other. I'm going to take my van to him after I "hiccup" around in Canada for a week for work.

Unnerving is a good description. It's like the engine is going to drop out for a very brief second. And like you, I believe this has been going on since I bought the van with 150K on it!

[mountainhick]

I meant Samie in my previous post (he is the Previa guru in the PNW). He has seen this many times and thinks it's the throttle body positioning sensor/butterfly something or other. I'm going to take my van to him after I "hiccup" around in Canada for a week for work.

Unnerving is a good description. It's like the engine is going to drop out for a very brief second. And like you, I believe this has been going on since I bought the van with 150K on it!

Hey, definitely post the outcome.

I really want to cure this.

[timsrv]

Maybe somebody who knows Samie can convince him to join TVT . Tim

[Steve C.]

Just wanted to post a follow-up to this issue. It may have been solved simply by replacing the spark plug wires with a new set combined with a newer distributor cap that I put in a few months back (but new DC wire in this last round). I drove the van about 100 miles on the highway this weekend and did not have the THUNK so I'm crossing my fingers that it's fixed!