Drives fine, Surges at Idle + OBD Code 85 - UPDATE: RESOLVED!

[BoostedE21]

Hi Folks,

I replaced my heads today, got everything reassembled and the car runs extremely well except for at idle.

When the car first starts, for about 5 seconds all is well - when it then idles down, it starts to surge between about 400 to 700 rpm with a very consistent rhythm. This happens when it's cold and warm. No trouble starting, no trouble driving, just at idle.

I also now have a OBD Code 85, which is "Canister Purge (CANP) Circuit Failure". I don't recall this being present before the disassembly/reassembly, and am not sure if it's related.

I have checked for vacuum leaks in most places by spraying brake cleaner on the connections, and didn't notice any change in performance.

I read that this could be the PCV Tube on the bottom of the throttle body...There's a little plastic "L" piece that seems to crack frequently, and that could create a vacuum leak that I didn't check.

I also read that the common solution here is the IAC valve - I am picking up a replacement in the morning to see what that does, but my current one appears to be operating fine, so I'm not convinced that'll resolve my issue.

Any other ideas of things I should investigate would be appreciated!

 

[BoostedE21]

We were able to resolve this quickly - just wanted to post the results in case anyone else experiences this combination of issues.

The throttle body sensor connector was not plugged in all the way. After brushing the connector and re-connecting it, the idle smoothed out and the CEL went away!

 

[1991 sploder]

We were able to resolve this quickly - just wanted to post the results in case anyone else experiences this combination of issues.

The throttle body sensor connector was not plugged in all the way. After brushing the connector and re-connecting it, the idle smoothed out and the CEL went away!

Check that purge valve while the engine is running. Hold it should click and stuff ECT open and close on new cars it's like a main part...yea the truck will run good without it but if u have an original it's most likely not working... Check the canister it's attached to needs fuel vapor I've heard fools pour gas into them to get it started.... I love this part because it's like mini nitrous sucks up fuel vapor at high rpm..
Noticeable difference with it fully functional.

 

[BoostedE21]

Check that purge valve while the engine is running. Hold it should click and stuff ECT open and close on new cars it's like a main part...yea the truck will run good without it but if u have an original it's most likely not working... Check the canister it's attached to needs fuel vapor I've heard fools pour gas into them to get it started.... I love this part because it's like mini nitrous sucks up fuel vapor at high rpm..
Noticeable difference with it fully functional.

Which purge valve and canister are you referring to? Where are they?

 

[1991 sploder]

U posted in stock 91/94 it's going to be driver side fender attached to a black rectangular box with a vaccum line going to octipus on the intake manifold.

 

[1991 sploder]

Up next to the core support probability just dangling

 

[1991 sploder]

Lol let me back up just a tad bit...u would probably get a kick out of this....the 1991-1994 explorer is like a new car. You have aluminum heads ECT ECT ECT now the new cars have mass produced components wont last as long... Anyway alot of people have it twisted it's a modern engine with just a obd1 connection... U should do all sorts of things new cars do... Top tier low oxygen fuel. 7500 mile oil change intervals... purge valve.... Ford was about 5/10 years ahead when this vehicle was made...nobody understands needs to be taken care of like a 2004 not 94... Granted ford did use the ohv design but in 91 when this came out it was like very advanced...come on push button 4wd auto hubs and a rear wiper with a sub.anf the glass pops open..in 1991? GM cant even do that now....its a new car