The question is in the title. To make a long story short I reset the throttle body set screw and I think after sitting for a few minutes I am still getting a code 35. The car is now idling about 1000rpm on the tack give or take 100rpm. Do I need to disconnect the battery to reset the ECM too?

Here's the long story:

I've been working on the car for weeks trying to get it road ready again. I bought it last fall and got to drive it for a couple of weeks before putting it away. It had 73,000kms on it but it ran and drove and was in pretty good shape other than the obvious areas where it was mucked with (which I thought were mostly cosmetic). The car was driving, but it was driving with a stumble / miss at cruising and low load conditions that was getting worse the more I drove it. I decided that my winter project would be a full tune up and engine bay clean up.

I took the engine down to the lower intake to change the valve covers. Injectors were removed from the rail to clean it out. Cold start injector and throttle body coolant lines were deleted. Vacuum lines were re-done DIY with aluminum tubing (all connections zip-tied). EGR and throttle body both cleaned right out. New gaskets used everywhere that I took one out.

I had never been into an engine this far, and yesterday evening I got to the nervous / exciting moment of starting the car for the first time since parking it up on the stands.

After a couple of cranks the car started and revs were way up. Ok I thought, it just needs to sit and re-learn. Let it idle and warm up and eventually the idle settled at about 1400RPM. Then I remembered reading it needed to be driven to re-learn itself so I took it for a 20 minute drive in town and on the highway. The engine was smooth and driving very well. The bad news was the idle never settled and with my foot off the gas it was like I had cruise control when it got down to around 2,000 rpm. Leaving the car in gear while slowing and then stepping on the clutch the revs would bounce back up before coming back to 1400 rpm.

Baffled, concerned and frustrated I stared at it a bit. Read up on how to scan the codes and got a code 35 - high idle (no **** ! lol). Back in the engine bay I checked all of my vacuum line connections. All but 2 were zip tied so I fixed that and put it back in. Started the engine and no change in idle.

Busted out the propane torch and pointed it at all my vac connections and gaskets at the upper plenum and didn't notice a change in idle, but while doing so I did notice a lot of noise coming from the throttle body. It sounded like restriced air flow.

Thinking it was the vac line that plugs into the back of the throttle body I pulled the throttle body and made sure it was seated properly and re-installed it, that didn't change anything. However when leaning over the top of my engine I found that the throttle body set screw was not plugged like it should be. I know I didn't un-plug it, and not knowing how doing the work that I did could make such a dramatic difference I took a shot in the dark on a hunch, noted where the screw was set and turned the screw 1/2 turn to see what would happen. Instantly the idle dropped (and I smiled a bit). Another 1/2 turn, more idle drop.

So I come onto here from my cell and find the instructions for resetting the set screw. Bridge A/B on the connector, turn key on (hear clicking @ IAC), wait 30 seconds, pull IAC connector, start car. It's idling about 13/1200RPM. I adjust the screw down until looking at the tach it's idling about 600ish rpm (it sounds like its barely running) then shut it down. Pull the A/B jumper, reconnect IAC connector and restart the car. MUCH, MUCH BETTER! Now idling smooth at about 1000 rpm +/- on the tach. Tach is dead steady. No immediate CEL after a couple of minutes of sitting there. I jumped for joy, then I called the wife out and we went for the first drive of the season to my buddy's place about 30 minutes drive away mixed driving. He sometimes helps me with things and I help him work on his Mini.

The car drove great, rock steady, no jumping tach, no miss / stumble, awesome. I stopped in front of his house and let it idle for a few minutes to show off the engine bay work I did and after a few minutes the engine light was on again. I believe it was still idling at 1000rpm +/- on the tach. I was assuming it was the code 35 again. Bowing my head in shame I got back in the car to drive home and as soon as I accelerated down the street the light went out.

Is this normal? The light never came back on at any stop or at home when I was parking the car.

My questions is: did I reset the screw correctly, or did I miss a step? Was I supposed to disconnect the battery to clear the code? Because I definitely did not do that. Does the light come back on from memory in the ECM or did it think it was it still idling high? To be honest I can't remember if I checked the code back at home or not.

I didn't play with it any more after that. I was so happy with how it drove and I was so hungry / tired I went into the house right away. I wanted to get some people's take on it.

Thinking about it this morning here is the distributor issue that I found and corrected when doing my tune-up.

https://www.fiero.nl/forum/Forum2/HTML/127738.html

My guess is that the previous owner or his "mechanic" was having trouble getting the car to run with the distributor like that and used the throttle stop screw to open up the throttle body until the car would idle. That is also a shot in the dark. I did clean the throttle body and IAC when it was apart but don't see any other reason how I could put it back together the way it came apart and idle that much higher.

See my Cave, Idle Stop

Yes, DTC = ECM reset to clear
ECM will store code until losses power at ECM standby power wire.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

It sounds like you did it right. The IAC completely closes so your are only feeding air through the TB gap by adjusting the gap in the throttle plate. The IAC air air doesn't go through the upper plenum but rather a pipe from the TB down to the lower manifold. Check that for leaks.

If the conditions for the error go away, the light will go off but it will keep the error logged until you get 50 restarts without the error or you clear the ECM. Having the error in memory will not affect how it runs. If you are still getting the SES light, something is still amiss.

Did you take the IAC out and clean it? If it's gunked up and not sealing off it will leak some air and your IAC counts will be off and you will through that error (35.) Also, if that idle tube is leaking you will also through the code.

Redo the minimum idle adjustment again and recheck it. DO you have a scanner to look at the IAC counts at idle?

Thanks for the repliess guys.

Ogre, I did everything as you listed in your cave except I left my vac lines connected as oppsoed to removing them and plugging the connections.

I did clean the IAC plunger when I had it apart, but I believe I simply wiped it off with a damp rag and didn't use anything special on it. I can easily remove it to check it and clean it again. Is intake cleaner safe on it? I was afraid of harming it before so only used a rag. The internal passages were cleaned thoroughly with intake cleaner. That tube that connects to the lower manifold is the first place I looked for a leak. I actually removed the throttle body and re installed it to make sure that line was properly seated.

Unfortunately I do not have a scanner. I did what I've done already with my simple hand tools and the help of the forum.

I can re-do the minimum idle setting easily now, I just have to wait for the next day with descent weather. Rainy, cold, damp evenings for the next few days here. Should I reset the ECM before re-setting the min idle or after? Can I pull a fuse or do I have to disconnect the battery?

Thanks again for the assistance.

Awesome, I'm learning something new everyday. I'll reset using that connector.

Cheers.

quote Originally posted by Ry86GT: Awesome, I'm learning something new everyday. I'll reset using that connector. Cheers.

You'll need to go for a drive with some idle time to allow the ECM to readjust some stuff. Don't be surprised if the idle is wonky until you do. The ECM is always learning but when you reset it, it has to start all over. 20 minutes with several stops and 5 minutes of idle will usually do it.

quote Originally posted by Gall757: ECM reset connector

I don't know if there's a difference between different years, but I've found that simply disconnecting that "ECM reset connector" did not eliminate stored codes. I had to disconnect the battery momentarily. I've read over the years here that other people have reported the same issue.

I don't remember if it was with my '84 duke or my '86 GT, but it was indeed necessary to go the extra step to clear the codes.

Just wanted to update that I didn't get too exceited and wanted to try and drive the car again to give the ECM a chance to learn. At lights the idle now drops to about 975 on the tack and is rock steady. I'm thinking I'm not going to reset the ECM and I'm just going to leave it.

Now I have a busted VSS to deal with lol.