502 MPI Adj
 

95 502 mag mpi - idle adjustment -
there are 2 allen head screws in the bottom of the throttle body,
I beleive they are for adjusting each throttle plate -
can anybody help with the adjustment of these 2 screws ?

Problem is motor does not want to idle in gear. I believe these screws are out of adjustment. Have checked the IAC sensor, the TP sensor and they test fine. Please help.

:confused:

Don

Don, Im not positive on this but I think if you try to adjust idle on a computer controlled motor the computer will just reset back to the factory spec. i.e. turning the screws won't help.

Eric

Whoo, hondatv. I don't think these adjusters are going to change anything unless they are loose and have moved. There are other things that need to be checked. What about the MAP sensor? What about fuel filter? What about fuel pressure? What about timing? I don't mean to pessimistic, but I see alot of people chasing the wrong problem. There are alot of other things that can cause this type of behavior, such as a vacumm leak. OK so when did this start happening, or has it been a slow progression. What has changed since it idled ok. There are alot of great people on the OSO board with alot of knowledege. Many people here have probably had the same problem at some point in time, so if you can give us some info we will try to help you out.

Welcome to Offshore Only!;)

hondatv,

look for a little filter near the IAC motor. it might be dirty.
If so the IAC motor will just keep searching.

Is the IAC motor accessible by taking off the flame arrestor? I may need to check mine.

more info....
 

28 eliminator & others,

Motor idled fine last year, had to rebuild, motor is now 30 over,
same cam, added MSD box, MSD coil, EMI exhaust, ASM computer mod,
air filer and fuel regulator. Motor runs fine, idles fine in
nuetral. When put in gear idle is rough, wants to stall.

I tried adjusting the two screws for primary and secondary throttle
plates- thought would work like a carburator throttle plates.
Are there some type of spec for the adjustment for air to the IAC ?

Have tested the IAC, TP, MAP, fuel pressure, timing, idle and 3000
under load. All fine. Will have to check on vacuum (my guage is
broke). Thanks for all the help - this is a great site, lots of
knowledge.

Don

Don,

The idle is controlled by the computer. It regulates air flow through the IAC ( idle air control ) motor. The screws on the throttle plates are for adjusting minmum air. They should not be touched. I am not sure what they are set at, but I do know that trying to raise the idle that way will not work. Is it possible that Arizona Speed lowered the idle somehow when they re-programmed? Do you have another e.c.u. to try to see if it cures the problem? Another possibilty is that there is dirt under the i.a.c. Sometimes the air hole that goes from the i.a.c. into the plenum gets dirty, but I doubt it since you said the motor is fresh.

Thanks for a place to look. I did not take the TB apart there may be some trash in that hole. Will check and clean. I will also check for the filter that jdelo talked about. If I am understanding this right those 2 screws are linkags stops. When I adj those two screws I am opening or closing the throttle slightly, which tells the TP sensor that the throttle is open slightly, in turn tells the ECM the throttle is open slightly and allows the RPMs to raise.
I understand this is not the way the system is designed to work, but it's the only way I know to bring my RPMs up. It does bring my RPMs up but the motor starts to surge when I get to a certain point. I guess I can kick my own a$$ for ever touching those two screws. Anyone know how to adjust the screws (where should they be set)?

hondatv, I would call to ASM and ask to talk to the programmer about the issue. I would bet he will have some good ideas about what may cause this, and possibly programming also. As far as the adjusters, I don't have a clue how to adjust them, but I would try to get it back to a good idle out of gear like it was. If you are going to pull the TB, there probably is a setting of gap between the throttle plates and TB. I just don't know what it is, but I can look in my book and see if it is in there(that's a stretch).
I am pulling my TB off soon to put on a new one from whipple, so I could measure the gap on a stock one for you. OK back to the problem, what is the RPM at idle? If it is 600-800 then you don't want it any higher and air/fuel mixture seems to be the issue if it idles ok until you put it in gear. Or the timing maybe off, what is it at? A vacumm leak of any kind will cause this problem on any motor. Buy a new vacumm gauge it may tell alot. The little filter near the IAC motor might be a good place to look(Hmmmm I didn't know about that. Thank sjdelo) When you find the real problem, the adjuster settings may not be that critical.
Welcome to the fun world of troubleshooting!:D Do some messurments and give us the results, then we can help out more.

hondatv

Checkmat454MAG is correct. the ECU sends out pulses (counts) to the IAC. The IAC motor is supposed to match these counts.

If that air hole is dirty the IAC motor will just keep searching to match want the ECU is sending out. It is possible that ASM set the counts to low.


jdelo

I don't know if you have it figured out yet, but I have one other idea. Check the fuel pressure. If the vacuum hose is off at either the regulator or the intake it will shoot the pressure up way too high which could be causing some of your problem, especially if you have added an adjustable pressure regulator and have raised it any over stock. ASM should be able to tell you what pressure they want you to run with the programming they gave you. You may also want to check the plugs after a some running just to double check things.

I checked fuel pressure - 43 at idle/ 45 running, as ASM suggested. Talked with ASM today. The two screws control the throttle plates and play a role with the IAC valve. They recommended a diagnostic computer test of the CPU, setting the throttle plates to a 45/50 air count/pulses. They indicated if the screws are too far out of range the IAC would be unable to match counts and that would cause the problem. They also said any of the other things suggested here could cause the problem - got a new vacuum guage will test this weekend.

That pressure seems real high to me. Is that with the vacuum hose on or off? I was originally told by the first person to reprogram my ECU to run that high. Long story short, the program i recieved was not meant for my application. It would load up so bad at idle that it didn't want to run, then when i checked the plugs after a long cruise, they would be snow white from being lean. I ended up just eating the cost of that programmming and sent my ecu to Dustin Whipple where he told me what was wrong with the program that was in it and then reprogrammed it for me. The end result is that I am very satisfied. I only run about 35-36 PSI fuel pressure at idle (with vacuum on) and the new program raised my rpm's by about 300 which is a gain in top speed. When checking the plugs now, they are a nice light tan color as they should be. By the way, this is nothing against ASM or what they are telling you. I have never had them do any programmin for me. I am just explaining what I have been through. Hope you get it figured out.

i have done a ton of dev. work on this motor and still have some in serv. with a ton of trouble free bad ass run'n hours on them...fell free to cantact me by phone...for the next few min i am at 734 458 0924 (ford)
joey
f2-80

ps...some are telling u incorrect info.

I am interested in the correct info. Please share.

Audacity - I'll try calling again your phone's been busy.

Bill 3 - I had the boat out once this year on a long cruise - checked plugs after and they looked fine. Boat idles fine in nuetral, idle problem occurs in gear. Have checked plugs since - still look fine, even after idling in gear and motor cut off (slightly rich not excessive). What size motor are you running ? Factory stock for my 502 is 36 psi with vacuum on. I'm running a 502:
502 30 over (509)
Flat top pistons
Comp Cam 234-237 @ 50 .564/.566 112
Rectangle port heads w/pocket porting
Roller Rocker
EMI thunder exhaust w/long stainless risers
ST 450 mufflers
K&N air filter
Adjustable fuel regulator
ASM programmed ECM, they rec 45 w/vacuum on.

I appreciate all the info, will let it be known when the throttle plates are set and have vacuum checked..

Audacity, Please teach us all, tell us what is correct. Thanks.

bill 3 everything you said was correct

i loved mess'n with these motors...the idle was my largest problem though....finished product..... idled at 710-730rpms no more no less for hours!....it had to sometimes due to location. by the way the cam used way the hell larger than yours.

try this # 734 523 5339

Use a Merc. scan tool to monitor TPS voltage and IAC motor counts. The two set screws are the adjustments. Set the TPS to .66-.70 (about 650-700 rpm) with the primary set screw. Check the IAC counts and make sure they are between 20-40. If they are too low adjust the secondary throttle stop to close the throttle, if too high adjust to open more. Note- the engine must be turned of for 5 seconds and restarted to properly reset the learning of the IAC system.

Got It!
Borrowed a scanner, took it out Sunday, set the TP sensor and the IAC valve - motor idled at 675 instead of 800, in and out of gear.
Fuel pressure is set at 45, according to ASM specs, plugs are a little rich, plan to try reducing fuel pressure and try again.
Thanks to all for all the help :cool:

Whereis the IAC located? My 6.2 takes 3 or 4 seconds to return to idle if I rev to 1000 rpm.

Great Job hondatv.:) I don't know everything about this stuff, but this is a great place to find the right answers. I'm glad you got the problem resolved, now for a good boating season.