rough idle; AIS motor available?

[87glhs]

Having a rough idle problem with an '87 TII motor.

When started (cold), it idles bad and has "fits" where it tries to stall, or revs up quickly to 1500 on its own.

If I step on the gas and rev the motor up it runs smooth.

Any other GLHS owners see this problem?

Also, who sells a replacement AIS motor? Looked at Advance and NAPA, but the ones on their site don't look right.

Thanks in advance--

[black86glhs]

Yep, mine does it, too. Ralph mentioned his T-III daytona did this and he plugged the line to the purge valve and his stopped. Haven't tried it on mine yet.

[IROCNOROLL]

The condition you are describing is a vacuum leak. When you open the throttle, the hole you are providing for air flow past the throttle plate is bigger than the vacuum leak, so the surge disappears until the throttle is closed again. The vacuum leak is allowing more air into the intake than the IAC passes, and that limits the IAC from controlling the idle and warm up high idle rpm correctly. Fix the leak. Fix the surge.

[IROCNOROLL]

Yep, mine does it, too. Ralph mentioned his T-III daytona did this and he plugged the line to the purge valve and his stopped. Haven't tried it on mine yet.

Sometimes the Charcoal Canister becomes saturated with fuel (usually a condition caused by always filling the fuel tank to the top of the filler tube every fill up) and the system pulls the more concentrated than normal fuel vapors collected in the CC thru the purge solenoid, to the intake.This can also mess with the idle rpm, and appear to be a faulty IAC.

A purge solenoid, or any other vacuum controlled solenoid can also fail and become a vacuum leak to the intake. A waste-gate control solenoid is normally open and vented to atmosphere. That is why the pressure source for the WG control plumbing is taken from the nipple on the side of the compressor housing and not from the intake manifold. Anything in front of the throttle plate is atmosphere to slight positive pressure from the turbo wheel basically spinning all the time the engine is running.

Anything connected to the intake mani after the throttle plate is exposed to vacuum at idle. If the WG control is connected to vacuum after the t/plate, and the control, even a MBC, is normally open like the OEM WG solenoid is, then you will have a vacuum leak at idle. This is the primary reason you source that circuit from the compressor housing, and not from the manifold.

FWIW, The theory that sourcing the boost control from the mani side for a better read on the actual boost after the losses thru the plumbing and a FMIC is fine, except it really doesn't matter. As long as the boost gauge is connected to a mani source, the settings used for the MBC are based on the pressures read there. By using the pressure source on the side of the compressor, there should be a restrictor in line to limit flow "volume" losses, without limiting the pressure applied to the WG can when the controller dictates. Also this prevents the WG can from "seeing" negative pressures or vacuum at any time. Just makes for a more consistent control, and reduces the opportunity for big turbo surges and spiking. When the circuit has to deal with vacuum and then pressure build before the boost control works, there is more time delay in the control and more real time opportunity for the spike condition to happen. Surge can be a condition of too large of a hose to the WG can and the pressure source taken from he manifold instead of the compressor housing source. It is sourcing a wider range of vac to pressure cycles, and with a larger hose the extra volume of air moving thru the various up and down pressures, causes the WG can to be cycled too far on and off. Kinda like an old Ford truck with a worn out front end cruising down a rutted road. You have to really work the wheel back and forth to keep it sorta pointed where you want it to wind up. Same with the WG control pressures. Think it thru. Like I said... FWIW

[Force Fed Mopar]

Could be a bad speed sensor too (although that usually throws a code).

[black86glhs]

Thanks for the info. On mine, the surging goes away after 20-30 seconds. Since it goes away, I was thinking bad charcoal canister. It is an original 86.
I want to redo my wastegate plumbing. The only problem with what you describe, is that some don't have the fitting on the compressor housing. Early cars didn't have that. Sorry, not trying to hijack.

[IROCNOROLL]

Thanks for the info. On mine, the surging goes away after 20-30 seconds. Since it goes away, I was thinking bad charcoal canister. It is an original 86.

The cpu usually vents the CC only during cruise conditions, and closes the solenoid at idle and WOT. Now if the solenoid is stuck in the CC vent position, it will "pass gas" anytime the manifold vacuum is high, like at or close to idle.

Simple enough to pull and plug CC purge and see if the surge is still happning.

As long as the MBC has a venting relief hole on the WG side, a simple check valve in the source line from the mani to the MBC would prevent the can from seeing negative presssure (vacuum). It might slow down the boost control reaction time for the can though.

Of course... a handy clever kind of guy might just drill and tap a 1/8" pipe thread hole into the output side of the compressor housing and take the MBC signal from that. With a say roughly .030" - .040" restrictor in the line before the MBC, of course.

[IROCNOROLL]

I wonder what happens if the CC purge solenoid is stuck open, and you apply boost to the tank thru the CCP line. Sealed cap = pressurized tank = pressure on the return line. This would restrict the fuel return, and should raise the running rail fuel pressure, in theory.

[87glhs]

Thanks for all the insight and replies. As far as vacuum, I haven't seen anything obvious--if there is a leak I would have to guess it might be a blown gasket on the intake somewhere. Any takers on this one?

Also, has anyone had to replace their AIS motor? When I turn the key on I am hearing it shriek once in awhile and I wonder if it's not starting to hang up.

I can't seem to find an after-market replacement for it--any thoughts?

[89ShelbyGuy]

Hey, i just had the same problem on my 89 daytona t2, i also thought ais motor, so i just put one from a 52mm tb, and it didn't cure the problem, the problem was the exhaust donut connecting the swingvalve to the d/p. make sure you don't have any exhaust leaks there. I replaced mine and no issues anymore. My symptoms were: After starting it up either cold nor being warm is would idle at 1000 rpm, then just chugging out to about 500 then the computer tried to compensate for it and my rpm shot to 1500..then settled back down and it was a constent process. It never died on me, it just was annoying.

[JDAWG]

You can buy a new AIS at the dealership

[black86glhs]

The cpu usually vents the CC only during cruise conditions, and closes the solenoid at idle and WOT. Now if the solenoid is stuck in the CC vent position, it will "pass gas" anytime the manifold vacuum is high, like at or close to idle.

Simple enough to pull and plug CC purge and see if the surge is still happning.

As long as the MBC has a venting relief hole on the WG side, a simple check valve in the source line from the mani to the MBC would prevent the can from seeing negative presssure (vacuum). It might slow down the boost control reaction time for the can though.

Of course... a handy clever kind of guy might just drill and tap a 1/8" pipe thread hole into the output side of the compressor housing and take the MBC signal from that. With a say roughly .030" - .040" restrictor in the line before the MBC, of course.

I wasn't sure when it did it. I thought some did it a few seconds after start up since they are running rich during cold start up. In other words, the fumes from the canister would enrichen slightly, which is fine on cold start.
Mine idles at 18-20 inches of HG, even cold. I'm not saying your wrong, but if it vented at high vacuum, it would do it all the time. I still need to check it. I'm still also running stock setup. I was looking at adding the fitting to it, but it is still in the car and I dont feel like messing with it just for that. WHen I get the CB built for it, thats a good time to do some fooling around.

[87glhs]

Hey, i just had the same problem on my 89 daytona t2, i also thought ais motor, so i just put one from a 52mm tb, and it didn't cure the problem, the problem was the exhaust donut connecting the swingvalve to the d/p. make sure you don't have any exhaust leaks there. I replaced mine and no issues anymore. My symptoms were: After starting it up either cold nor being warm is would idle at 1000 rpm, then just chugging out to about 500 then the computer tried to compensate for it and my rpm shot to 1500..then settled back down and it was a constent process. It never died on me, it just was annoying.

That's exactly what it's doing--I'll check it out. Assuming it is leaky I wonder what it would be affecting to cause rough idle--O2 sensor, or just plain backpressure?


You can buy a new AIS at the dealership (JDAWG)

I wasn't sure if it was a dead p/n--seems like 90% of the parts now are gone, I'll check. Advance has some AIS motors at their site, but none appear (they also list OEM p/n cross-ref) to be a match.

[JDAWG]

this is the pn 4861086

[IROCNOROLL]

I wasn't sure when it did it. I thought some did it a few seconds after start up since they are running rich during cold start up. In other words, the fumes from the canister would enrichen slightly, which is fine on cold start.
Mine idles at 18-20 inches of HG, even cold. I'm not saying your wrong, but if it vented at high vacuum, it would do it all the time. I still need to check it. I'm still also running stock setup. I was looking at adding the fitting to it, but it is still in the car and I dont feel like messing with it just for that. WHen I get the CB built for it, thats a good time to do some fooling around.

Ok... To quote the manual. Purge Solenoid... Used on all EFI engines, 1984 and up. This allows the LM or SMEC the control of shutting off purge "when cold or in boost."

Also... if this engine is an EGR equiped '84 - '86 turbo, there may an issue with a sticking or worn EGR valve shaft allowing the intake to have essentially egr flow when it shouldn't happen, OR a vacuum leak source that will be pretty noticable on cold start when enrichment needs to be higher. This type of leak will also contribute to a cold start surge at warm up RPM. Again, once you open the throttle, the flow past the larger vacuum leak you have created at the t/plate covers the unmeasured source, and things smooth out as the TPS tells the cpu to add fuel.

[black86glhs]

Ok... To quote the manual. Purge Solenoid... Used on all EFI engines, 1984 and up. This allows the LM or SMEC the control of shutting off purge "when cold or in boost."

Also... if this engine is an EGR equiped '84 - '86 turbo, there may an issue with a sticking or worn EGR valve shaft allowing the intake to have essentially egr flow when it shouldn't happen, OR a vacuum leak source that will be pretty noticable on cold start when enrichment needs to be higher. This type of leak will also contribute to a cold start surge at warm up RPM. Again, once you open the throttle, the flow past the larger vacuum leak you have created at the t/plate covers the unmeasured source, and things smooth out as the TPS tells the cpu to add fuel.

The EGR is there, but the egr tube is gone. The EGR is plugged, but that doesn't mean it isn't leaking. I tried the purge, no go. The EGR is next. It hasn't bothered me all that much, more curiosity on what is happening. Besides, I've heard from many others that many of them do it. I have the generic AIS from the auto parts store in it, so that may even be the issue.