Engine Stumble [Video link]

[wizardsandunicorns]

Hey,

1989 240 DL wagon here, with a video link to the issue. I can reproduce this issue exactly, the video was taken on the 3rd cold start. https://www.youtube.com/watch?v=GBdeoqXebYc

I SUSPECT it's an airflow problem. The engine turns and runs on a dime but then chokes out (it seems). I've cleaned the MAF sensor and the IAC and am probably going to clean out the throttle body as well. Before cleaning the IAC it would die on ignition if I didn't hit the gas. Now it runs and stumbles as shown in the video. My brother believes I might have to replace the presumably defective IAC but I can't be sure so I thought it was a good time to post this. Would love to hear some thoughts



Thanks

g.

[RickHaleParker]

Go ahead and clean out the Throttle body. Very well could be gunk on the walls of the Throttle body restricting idle air flow. The IAC valve is designed to work withing a certain range. Restrictions in the throttle body can push the combined air flow out of range.

Cleaning the Throttle body will not waste time and money. It should be cleaned periodically.
Replacing a IAC when the problem is a dirty Throttle body will waste time and money.

[wizardsandunicorns]

Yeah! I cleaned the TB out well, it had lots of gunk in it but didn't change the problem unfortunately but feels good to have it cleaned. 30 years of gunk. Yeesh.

I'm going to attempt some electrical tests on the IAC and also inspect the temp sensor as well, the problem still seems to be isolated. As soon as I give it some gas it stumbles to a stall.

[RickHaleParker]

As soon as I give it some gas it stumbles to a stall.

Sounds like lean on run.
Make sure the IAC is switching off when you touch the throttle. Check for Air leaks on the intake side ... smoke test.

[wizardsandunicorns]

I will do that! Thanks for the feedback.