22er idle problem after engine swap.

[joostio]

I have the strangest idle problem that so far completly confuses me.

I recently bought an 85 4 runner and blew up the engine. the engine ran and idled fine before the engine problems. easiest solution was a motor from the wreckers. I found an 86 22r, no intake or exaust manifolds. I installed the motor and bolted up all my original intake and exaust. ( there were many problems along the way but none related to idle ) I installed my original distributor and I think most of the vacuum hoses are on the right spots.

The truck fires up right away ( yay! my first engine swap and it runs ) and idles fine for a while, I take it for a short drive, less than 2 min and the idle problem presents itself. when the brake pedal is applied the idle drops drasticlly to the point of almost stalling, then comes up again and drops again in a cycle until the brake pedal is released. then it idles normal again until the brakes are applied again. I thought it might be related to vacuum lines and the brake booster, but when I disconected the brake booster vacuum line it still had the idle problem with the brakes applied. The next thing i tought was to find out if the problem was related to the brake light switch, I depressed the pedal by hand and held the brake switch in the pedal up postion. this made for no idle problem, until I released the brake light switch. So some how this is an electricle problem. so I ran some temporary grounds to the engine and distributor, no difference.

so the question is "Why does my truck idle funny when the brake lights are on?"

[Pony]

You have a vacum leak the reason the truck dies off when you put on the brakes is beacuse the vacum that the brake booster is useing robs the engine of the vacum it needs to operate properly get a manual with vacum diagrams and start chasing.
That or the alt is hooked up wrong or shot efi needs a certain amount of volts to run normal does it do it when there is a draw from somwhere else ie headlights on/off etc etc?

[HobiesBestFriend]

http://forum.ih8mud.com/showthread.php?t=155085
might help

[joostio]

it runs fine with the headlights on, it also runs fine when the brake booster vacuum line is disconected. it only does the problem when the brake light switch is activated.

[joostio]

still doing it but more info. the truck does not have the idle problem when in 4 wheel drive, only in 2 wheel high, of course with the brakes on. go figure?

[intimidator]

have you check the grounds that are associated with the circuit. find an EWD and start back tracking, might be something dumb like a bad shared ground somewhere.

[joostio]

I am fairly conviced this is an engine swap issue because it ran well before the swap apart from the blown head gasket. it did sit for 2 months before the swap happened and I guess something could have happened then but I don't think so . strange problem.

[jjamieson]

did you put the small ground wire on from the firewall to the head. also check the main ground from the batt to engine (bigger size wire).

[Uncle jesse]

on the vacume line going form the intake to the brake booster there in a one way check valve might want to make sure that it is still on there or is workin properly ..if it fails that would give you a hefty vacume leak and might account for your idle issue

[jones]

When you press the brake pedal the ecu is supposed to idle up the engine to account for the extra load. The brake light switch actually sends a signal to the ECU to tell it that the brake is being pushed. The ecu is set-up to do the same when the AC is turned on as well.

I would guess that there is a bad connection between the switch and the ECU that is causing the problem. I would start by examining the wiring in the area to see if it has been damaged.

If you just want to fix it you could cut the brake wire where it enters the ECU plug. It will not idle up like it is supposed to, but I bet it also causes your problem to go away.

The wire that you're interested in should be green with a white trace. The thing is there are two wires going to the ECU that are this color. One is for the cold start injector and the other is for the brake switch. You have to figure out which is which. The cold start injector wire will run to the ECU plug who's wires go out into the engine bay. The brake switch will be in the plug where the wires stay in the cab. You might not be able to tell which is which though.

I would use a multimeter to figure out which is the correct wire. Put it to the resistance setting and put the 2 probes together to make sure the display goes to zero. If it goes to zero it tells you there is a connection. Then hook one probe to the green/white wire on the brake light switch and connect the other end to one of the two green and white wires at the ECU. If the display goes to zero you've located the correct wire. Give it a snip and see if it makes a difference. Make sure you can hook the wire back up if needed though.

Good luck.

[dp4125]

i had the problem on my toyota after putting in a new head gasget. i found it to be the intake manfold to be leeking in the rear of it.

[501]

When you press the brake pedal the ecu is supposed to idle up the engine to account for the extra load. The brake light switch actually sends a signal to the ECU to tell it that the brake is being pushed. The ecu is set-up to do the same when the AC is turned on as well.

I would guess that there is a bad connection between the switch and the ECU that is causing the problem. I would start by examining the wiring in the area to see if it has been damaged.

If you just want to fix it you could cut the brake wire where it enters the ECU plug. It will not idle up like it is supposed to, but I bet it also causes your problem to go away.

The wire that you're interested in should be green with a white trace. The thing is there are two wires going to the ECU that are this color. One is for the cold start injector and the other is for the brake switch. You have to figure out which is which. The cold start injector wire will run to the ECU plug who's wires go out into the engine bay. The brake switch will be in the plug where the wires stay in the cab. You might not be able to tell which is which though.

I would use a multimeter to figure out which is the correct wire. Put it to the resistance setting and put the 2 probes together to make sure the display goes to zero. If it goes to zero it tells you there is a connection. Then hook one probe to the green/white wire on the brake light switch and connect the other end to one of the two green and white wires at the ECU. If the display goes to zero you've located the correct wire. Give it a snip and see if it makes a difference. Make sure you can hook the wire back up if needed though.

Good luck.

is there anything you dont know?

[jones]

Oh, there's plenty that I don't know shit about. Ask me about a jeep.

[joostio]

found out on Pirate that this is a normal condition, when the idle is too high, the ecm cuts out the injectors when braking to help stop the vehicle. I must have some hoses hooked up wrong giving me a high idle (screw turned all the way down/out). might be a bitch trying to figure this out, can't find my before removal pics, crap!

[intimidator]

i'll flip through our service manuals at work and see if i can dig up a vacuum schematic to try and help you out