[1991shelby]

I have a 1991 daytona Shelby w/ 2.5 t1 5 speed.
I have recently started to have a problem with my AIS. One second it is stuck open the next it is closed. Sometimes it works fine. It is all over the place with no reason. I have replaced it and still the same thing is happening. For now it is unplugged in the closed position and I have to create a vacuum leak to start the car untill it warms up. Once it warms up I plug the leak and then it will run OK. I do have a few other problems that might or might not be related. I think it slipped a tooth on the timing belt. My tach goes in and out. Every once in awhile it will miss on a cylinder (probably timing). Random spark knock ( sometimes it will happen @ 5 lbs. boost other times I can run it to 14 lbs with no knock( within seconds of each)) My friend who is a mechanic but does not work on turbo's too much thinks it may be my ECU/ ECM is going bad. Any Ideas???:bang head:bang head
Thanks

 

[mmtphoto]

Any codes? Did you try to reset the AIS? take it off and clean it?

 

[1991shelby]

No codes even though the AIS is unplugged. Yes I tried to reset it and after I did the first time I got above 1500 rpm it opened and stuck. Then I took the car back home, tached it up a few times untill the AIS closed and the idle dropped back down then hurried up and unplugged it.
I took it off and cleaned it well (it actually shined) and replaced it. Same results.
I also put one in from a spare upper intake I had bought. Same results.

 

[NAJ]

First if you think the timing belt jumped you should be there first, that will throw every system out of whack.
Second, is there any idle fluctuation with the vehicle at base idle(as you have it now) and what is base idle speed?
Third, you say you have a misfire, be sure all basics are correct, plug gap/condition, ignition wires are not open/high resistance(5-7 k ohms per foot) or arcing to ground or each other, distributor cap is not cracked or moisture present. Use a spray bottle with water to spray the ignition components to see if the miss becomes more prevalent.
The basics have to be correct before you can even consider looking at the computer control system if there are no hard faults set.
Are the throttle plate and AIS passage in the throttle body carboned up? You replaced the AIS but if the pintle is sticking in the bore it will never idle correctly.
Is the PCV system clogged or do you have a collapsed or cracked line/grommet? The PCV is a metered vacuum leak that is calibrated into the controllers programming for idle control.

 

[1991shelby]

I agree. I want to hit first things first and to me that would be the timing.
Right now base idle is 958 rpm.
Ignition was the first thing I checked when I started to feel the miss - New plugs (gap was set to factory specs. AC Delco)- No apparent damage to the cap and rotor( both cleaned when checked)- Magnacore wires- Msd coil
I will spray down the system to check. The one thing I did notice is that the distributor seems tight but oil is leaking out of the base. My guess is that the oil could have started to damage the HEP. I have another dist. with a new HEP that I will clean and try.
I have cleaned both the throttle body and the AIS passage well.
There was alot of vacuum line work done on this car before I bought it. But I checked and replaced the PCV valve and all the connectors/ lines going to it( I did find a leak but this was prior to the AIS problem).
Thanks for your input. I really appreciate it.

 

[NAJ]

I see a problem already, base idle(minimum throttle plate opening with AIS at 0 steps) should be 550 - 575 RPM's. If someone moved the base idle screw the TPS may be out of range for idle which will cause your idle searching condition.
Be sure there are no vacuum leaks, a vacuum leak will create a high idle condition, it allows additional air to enter the engine, the MAP see's the additional air and the controller adds more fuel(increases injector pulse width)more air + more fuel = higher idle speed.
I would definatly check the vacuum system first before you jump headlong into the engine and lose sight of the cause of the problem.
Checking the vacuum lines and routing is a time consuming project and will require patience but I think that is where your problem lies.
If the plastic vacuum harness is still there thoroughly check the lines behind the valve cover for cracks/breaks, this is a common place for failure and sometimes hard to locate, you may even break a few checking.
Let me know if you need the vacuum diagram.

 

[1991shelby]

My friend hooked it up to his Snap-on Computer and could only get the idle down to the 758 mark before the engine wanted to stall. That was when we found the first leak. I really need to take some time and go threw all the lines. There was a breather added. The air intake hose was cut and had an insert with an extra vacuum port added. Peices of blue line have been added.
I still have the diagram that was under the hood. Don't supose you would have any idea amounts and sizes of hose to redo all the lines. I know it is a long shot but I figured I would ask since I live in the middle of nowhere and it takes a while to get to an auto parts store ( not just a quick trip).
The wierdest thing to me is how when coming to a stop light ( in neutral or foot on clutch) the car will hold an idle of up to 2700 rpm then drop down then back up ect. (yo yo effect).
I just bought a 89 2.5l turbo Aframe, engine,trans, pretty much the whole front end that I can get some of the orfices and check valves off of for the lines.
Thanks again for your help
I think this is going to take awhile.

 

[1991shelby]

Well I think I just found out where my vacuum leak is at. I was playing with the lines and could not find any but when I moved some of the injectors the hiss got softer.

 

[NAJ]

The sizes for vacuum and emission hose range from 5/32 - 11/32 and the biggest problem is the fittings, some are different sizes on each end.
I went to Pep Boys, bought all kinds of line and vacuum fittings and I keep them here just in case.I do not want to run all over town looking if something happens, better to buy a lot and have extra for later than not have enough.
If you live in the middle of nowhere you may want to check online, I find all kinds of bargains on eBay in "buy it now".You may find a complete vacuum tee assortment for a good price and you do not have to leave the house.
I am starting body work and needed wet sandpaper and found 25 sheets each of 400, 600,1000 for $2.77 each pack and shipping was only $7.00 for all.
When I first had my valve cover off about 10 years ago the plastic lines broke/cracked and I was about 3 hours in the dark just trying to get the VNT solenoids routed correctly so yes it is time consuming and a PITA but if you take your time and keep the lines neat and organized it will be much easier if one breaks next time and you will be more familar with what is there.
On a positive note you get to develope a very close relationship with your car by spending a lot of time together.

 

[NAJ]

Injector o'ring kits are available.
Vacuum leaks of all kinds will create havoc with our cars.

 

[1991shelby]

Well I will start with the injector o-ring kit, then check the timing. Hopefully there are no other leaks and I can start replacing vacuum lines one at a time. I do have quite a few Tees and other fittings from the other engine and other upper intake. This way my car is not down for any lenght of time.

 

[1991shelby]

I replaced the o-rings and it seemed to help. The old ones were pretty bad. My boost seem to come in faster and my a/f gauge did not jump nearly as much. I also found another vacuum leak. I was pulling vac. through the dipstick tube. My dipstick did not have a rubber groumet in the top. My AIS worked good for about 25 miles and then stuck allitle again. Hopefully stopping the leak through the tube will do the trick.
I did have one wierd thing happen. I am getting spark knock at 7 lbs. of boost but only in 3rd gear, like clock work. I do not get any knock in any other gear even at 15 lbs of boost. Seems very wierd to me.

 

[1991shelby]

Ok I have fixed any vac. leaks. Checked all the the vac. lines. both ignition and cam timing was off. Both were set. Now the car runs pretty strong even for having 176,000 miles on it.
The AIS is still sticking, opening and closing at any time. Anyone have any ideas where to look next?

 

[NAJ]

Bring the vehicle to base idle and disconnect the AIS.Be sure base idle is correct and see if the engine still surges with the AIS out of the system.If it does there is still a basic problem.If not you will probably need a scan tool to look at sensor values while the problem is present, you need to see what the controller is seeing.
Tap into the O2 Sensor signal wire and see if the voltage is crossing above and below
.450 volts and is staying in a range of .250-.750 volts, then you will see what the controller is seeing for fuel control.
Also backprobe the TPS between the signal and signal return line and see if the voltage is steady.

 

[1991shelby]

The engine does not surge with the AIS disconnected. I will hook up the scan tool again. We did check the TPS and it was working properly. I would like to recheck the O2 sensor and focus more on it.
I will keep everyone posted.
Thanks.

 

[1991shelby]

Hey NAJ could you please post the vacuum diagram. I do have the original under the hood but it would be so much easier to follow if I did not have to look up at the bottom of the hood constantly.
The guy before me made a vacuum nightmare for me. I already found a check valve (broken) in the line to the wastegate solenoid. Who knows what eles he did so I need to start all over.
I appercaite it. Thanks

 

[NAJ]

 

[1991shelby]

Vacuum lines are changed (i am pulling 22-23 at idle). O2 sensor is working properly. AIS still opening and closing at will but seems to be limited to about 5-700 rpm. It does not get stuck higher than 1700 rpm but still flutters.
I was told that the speed and distance sensor will drop idle down when the car comes to a stop. I have experienced this in my car (aprox. 500 or so rpms).
So does the SD sensor tell the computer to do this by closing the AIS?
Are there any other signs the SD sensor is going bad? (my speedo sticks sometimes but just thought it was age)
I am trying to find the most likely route to test first.

Thanks

 

[NAJ]

You need to connect a scan tool so you can look at all engine control values and see what the controller is seeing, you will also be able to see AIS steps.
The controller is seeing something that is causing it to move the AIS in and out.

 

[1991shelby]

Since the scan tool needs to be scrolled through to look at different sensors just trying to see what to check first and then go from there. Besides just learning more about how my car works. I can rebuild a chevy v8 and a Holley carb but when it comes to the highly computer controlled cars I need more work.