EFI idle surge revisited(long)

[bronco-billy-66]

Well here we go again. I thought I had my surge problems fixed, but I was wrong. Here is what I have. 351w. Truck lower. Bc adapter. Car upper rjm harness. All stock parts. Fuel pressure is 39 at idle. Timing set at 10 with spout disconnected. At tdc the narrow vain on the distributor is pointed at the pickup thingy. I've done the set base idle procedure. And tps voltage is .98v. I've cleaned the maf. Pass side valve cover is hooked to the TB. Drivers side valve cover Has a pcv and is hooked to the bottom of the upper. I've sprayed carb cleaner all over this thing looking for a leak.
It runs really good driving and off idle. Fast idle is fine. It's just when the idle settles to around 700 or so it will idle for a minute then start to surge. And if it is idleing and I drop it in gear (c4) it will stumble for a second and then catch up(sometimes)
The motor ran really good with the carb. But it is well worn(good bit of blowby). Is this my problem?
I don't want to but do I need to pull my intake and look for a leak? Would that cause this problem?
I am at my wits end with this thing. What do you guys think? TIA

 

[Broncobowsher]

What does it do if you back the base timing down to 8°?
Could just be a touchy combo?

 

[bronco-billy-66]

What does it do if you back the base timing down to 8°?
Could just be a touchy combo?

Dunno. Never even thought about trying that. I'll try advancing it too. I ran it at about 14 with the carb. Does that matter? I thought the computer needed 10* to do it's thing. Worth a try. What else y'all got? ;D I really don't wanna pull the intake

 

[Viperwolf1]

You can check for a vac leak under the manifold. Pinch off the PCV valve hose so it can't pull vac. Make sure valve covers and dipstick are sealed up tight. Pull the vent line going to the TB and hold your thumb over it while the engine idles for about a minute or so. Pull your thumb off the hose and see if there's vac.

 

[fromme]

Two things that I would do first are:
1. Put a vacuum gauge on it so you know what it is at idle and can also read it when driving under load.

2. Try one of these:
http://www.latemodelrestoration.com/item/LRS-9939A

Sometimes with 351s the factory IAC has a hard time and fooling with this has helped me before.

 

[av bronco]

have you pulled the codes ?

 

[Bronco_69]

they make an IAC bypass plate. some call it the ranger bypass plate. i had to put one on mustang to stop the surge.

there are some pics of it in this post.

http://forums.corral.net/forums/showthread.php?t=1212646

basically it allows more air to bypass the throttle blade (kinda like drilling a hole in the throttle plate).

It seems to be helping the combo in my mustang. 351w, canfield heads, trick flow intake, tfs stage 2 cam. etc.

are you running the stock mass air and the 19's? are you getting fan wash on your mass air sensor?

here is one on ebay
http://cgi.ebay.com/ebaymotors/IAC-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

or summit racing
http://www.summitracing.com/parts/SDA-F2PZ-9F939-A/?rtype=10

http://www.tomco-inc.com/Catalog/29tabp spacer plate.pdf

 

[ransil]

you can get the idle bypass plate from a Ford dealer for around $35-40

 

[bronco_daddy]

all the signs and symptoms of IAC..usually just a cleaning helps but the replacement is cheap...just did my wifes V10 and now it is normal again. Wife V10 ran great but idle surged, especially upon start..many IAC issues are stalling motor after running solid

 

[bronco-billy-66]

Thanks for all the ideas.. I'm gonna try to get out there and look at all that today.
A few questions..

How would i seal the dipstick? It just has that hood thing that covers the tube, does that count?

How much vaccume should i be pulling at idle?

I'm a little confused, Ive seen the bypass plates before. Are ya'll saying that my IAC isn't providing enough air at idle? I pulled the solenoid off of it and when i pushed on the plunger the motor just revs up.. seems if it opens all the way (i dont know if it will even do that) it would give more than enough air. Im not really sure how that thing operates. Does it just flutter to maintain idle? If the bypass plate give more air at idle how would it ever idle at 650 ?
I really appreciate all ya'lls help. This thing is driving me batty%)

 

[Bronco_69]

i adjusted my plate to make the car idle at 750 with the iac closed. that way it would not go below 750. therefore no stall

it is not the best answer but it will work

 

[bronco_daddy]

One possibility is that the ECM (computer) is slipping in and out of open loop mode, which usually causes a change in idle control. Open loop means the ECM is NOT constantly correcting the air fuel mixture based on feedback from the oxygen sensor and instead uses a fixed algorithm to estimate fuel and air to the cylinders. Normally open loop mode ceases quickly after the engine starts, but if a sensor is malfunctioning or the oxygen sensor in the exhaust header is not reporting accurately, the ECM will continually struggle to find the proper mix, resulting in a surge or hesitation.

A stuck or faulty EGR will do this also

 

[RT]

I had a surge problem were I'd be stopped , foot on the brake and it would surge as if I was pressing on the throttle . It would come and go , and the check engine light would go on and off but never at the same time the surge happened .

I messed with that thing for weeks off and on until I pulled the connection off the water temp sensor for the EFI . The surge came back after reconnecting it .

This hasn't happened again since I replaced the sensor .

Pull the plug , it's a cheap check . Hope it works for you .

 

[bronco-billy-66]

Well... First off, thanks for all the help
I'm hanging my head in shame..:-X looks like in all my frustration working on this thing, I took for granted that my timing was set right. My timing marks are very hard to read and I had marked my balancer with a soap stone at 10*. But the timing was waaay advanced(the dist was tight).. I don't even know how it was cranking.. I cut a thin piece of masking tape so I could see my mark. As I was retarding the timing the idle came down to 400 or so.. idled smooth as silk..I reset my idle at 700, reset tps at .98v....now no surge. No stall. and the rpm's stay rock solid when I drop it in gear;D;D
I'm a happy camper, Now I just gotta get some miles on this thing
Again,Thanks for all the help I'm a dumb ass%)

 

[Bronco_69]

gotta love a happy ending