89 4x4 hesitation, I got codes

Ugh,

Ok so I was finally able to both borrow a timing light and get some time to actually dig into this issue. Timing appears to be ~20° BTDC regardless of whether the "Engine Check Connector" is jumped or not.

Consistent with my internal logic, I did things in reverse order of what Tim suggested and eventually learned that *mysteriously* the clamps on the throttle body side of the air intake hose were loose and thus not air tight. However, there was no change in timing after tightening everything down and verifying (with brake clean) that the hose was air tight. Van appears to run fine (at least no worse than before this all happened), but it's practically billowing smoke out the exhaust now.

The TPS has been replaced somewhat recently (under my stewardship and per Tim's TPS video) but it is an aftermarket unit. I haven't touched the ECU since purchase, is that the next likely point to test?

Thanks again!

- Perry

If no change in timing with the Check Engine Connector jumped, then it's a bad (or unplugged) TPS, a faulty harness, or a bad ECU. Even with the TPS being new-ish, I would still think that to be the most likely. Here's a post that shows how to check it without removing your throttle body:

https://www.toyotavantech.com/forum/...&p=395#post395

Not sure about the smoking thing. Not having electronic advance would not cause that. It could cause a code though and could lead to tripping that EGR temp sensor. Tim

Thanks for the link, Tim. I did some troubleshooting on the TPS and found I didn't have continuity at .022". I tapped on the TPS with a screwdriver and now it has a tone with the feeler gauge still installed; timing is now closer to ~12° BTDC and changes with the Check Engine Connector jumped so that leads me to believe the unit is starting to fail. I think running around with timing advanced the way its been also largely contributed to the weird smells I was getting from the exhaust. Replacement is in the mail hopefully this clears everything up. :sfr:

Yes, when electronic advance is disabled it can cause the exhaust to run hot. I've heard stories of exhaust manifolds glowing red after driving with that not working. I know it's not too much fun pulling the throttle body, and finding that gasket is not so easy either. Let us know how it comes out. Good luck :wnk:

I put a bunch of freeway and city miles on the van over the weekend and made it home with no hiccups or engine codes so I'm going to tentatively call this fixed. Thanks again, Tim, you truly are the man! A postmortem on the TPS showed a fair bit of corrosion on the connector prongs. I probably could have gotten away with simply cleaning the connector and the prongs on the TPS and reinstalling but I had already passed the point of no return when I saw this.

Side note, my Rockauto replacement TPS arrived with the tabs broken on the black plastic box and I had to swap the box over from my bad one. I'd never actually seen what the inside of a TPS looked like, it's surprisingly pretty straightforward. I wonder if these can be serviced in the future once replacement parts dry up and/or become prohibitively expensive.

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