Ok I have a 95 F-150 and it likes to surge at idle. I have replaced the plenum gasket and installed the service bulletin idle air control valve spacer so I can set idle. It has had a full tune up and new coolant temp sensor and map sensor. I have checked the TPS and tests good the egr is testing good and so is the egr position sensor. I also have put in a new air charge temp sensor. I am now up against a wall as to what might be causing it and as a mechanic it is driving me nuts I have been through all the tests that I could find on michell 1 and am just finding the problem. Does anyone have any ideas as to what I might be over looking. Once it warms it idles great and only surges once in a while. Thanks in advance

 

EGR could be carbon up!

 

Doesn't Ford recommend clearing the KAM after any ECC related component it replaced to rebuild the adaptive strategy learn table entries bases on present component config? By establishing a sys. currant draw by turning on the headlights and disconnecting the battery for at least 20 mins. to discharge the capacitor that protects the 128 bit memory where the KAM is stored. One reason is if a sensor has repeatedly failed or signaled out of range to the point that the ECC replaces that input w/ it's generic default value & that value becomes rooted into the learn tables. After that, although it is aware that the bad sensor has been replaced and it's output is now acceptable, w/o clearing the KAM, the ECC sometimes will ignore it & continue to use it's assigned value until a s**t load of warm up cycles have orrured with the new sensor correctly outputing before it will start recognizing And useing that output again and sometimes will continue to report the error code in cont. memory regardless of being cleared prior. Also to properly integrate any engine hardware mods like K&N'ing the air intake. When restarting, if curb idle settles down to within 150 rpm's of correct Idle rpm, I find it beneficial to establishing a smooth, solid idle, to continue the idle for 2 mins. then shut off for 1 min., then restart & place in gear w/ foot on brake & let idle for 2 mins.,and once again shut off for 1 min. Then drive the next 10 miles or so under lite load w/ smooth acceleration through the gears. On manual trans. sub A/C on for foot on brake while in gear, for emulation of idle under load. If idle at restart is really whacked, have someone disconnect the IAC valve and as the rpm falls, use the gas pedal to stabilize idle at desired rpm (It will argue with you at first,then you/ll notice it start to lock in and support itself at your target idle rpm) and then maintain for 2.mins. then shut off for 1 min. & reconnect IAC . then complete the procedure as you would have if the idle at restart had not been so whacked. This assumes proper EGR & Vac system function and TPS & IAC test good. Here's some related reading (scroll up the page of the link for article):How ECUs Use Closed-Loop Controls to Make Fueling Corrections v1.02 - Mazda Forums

 

mine was doing that too, i changerd out the air temp sensor ???? its on the front left hand side of the intake behind the air conditioning pump. $ sum reason i cant remember if thats the correct name of it but i had it and changed the other day and it hasnt seemed to do it. It cost like 20$

 

Make sure all your original plastics tubing for air cleaner and stuff if your if your MAF sensor is working properly and intake is leakin tighten all clamps ect.. if there is air leak anywhere it will get a fu##$% up reading could possibly be a
or intake gasket or manifold gasket leakin easy check spray starting fluid near around block to find your leak and different areas..

 

Ok First thanks for the ideas secondly I am a mechanic ASE certified and have done this for years My 89 I had was an easy fix but this one is wanting to be stubburn about it. My 95 F-150 with 5.8ltr A/T with P/S and A/C it stumping me. Here is the history sence I have had it. I replaced the map sensor and temp sensor they were out of range according to my Michell 1 data base ok. I checked for vacuum leaks that was first on my list, it does not have a mass air flow meter. I did a full tune up meaning cap, rotor, wires, plugs, air filter, pcv and fuel filter. From there I have replaced the upper plenum gasket so I could check the injectors under the plenum. I put the IAC motor spacer under it, this is a tsb from ford and allows you to adjust min. idle speed with IAC unpluged. I checked all other sensors and they are in spec. Thus here is were I pull my hair out. The compression is all with in 2 to 3 lbs of each other too so that has been checked also so now I untill I bleed or figure this out. Again thanks for you imput I will have to reset with the draw forgot about that one and see if it makes any difference. Otherwise if anyone has any more to add go for it as I am up to anything to fix it from here.

 

I will check the air charge temp sensor again just to be sure but it was in spec last check. I checked it first as that was what was wrong with the 89 I had. Any way thanks

 

Couple of curveballs :EGR tube or its connection at rear of engine leak. Brake powerbooster internal diaphram Vac leak. EGR diaphram leak. PVC seal grommet allowing flow to bypass valve. Unhappy childhood (sorry about that one. Just trying to think out of the box.) Have you ran KOEO & KOER scans or the ol' wiggle test? Maybe wander around engine components w/ unlit propane low flowing and see if something salutes w/reaction in engine behavior. Ready for this one: Intermittant/sporatic alternator voltage output voltage drops from impending internal diode crash or in reaction to condition of battery (bad cell).

 

Id try cleaning the throttle body then readjust min idle and check tps volts at idle. I know ford says dont clean the throttle body because you'll strip off the teflon coating. I guess they think when we fry eggs on the throttle body they'll stick. Make sure the port for the iac is clean too. If you dont want to spray the throttle body you can get a lot of goop off of it with a dry rag and needle nose pliers, but a toothbrush and gumcutter work better. Someone even makes a spray that is supposed to be teflon safe.

 

dup.................

 

. I put the IAC motor spacer under it, this is a tsb from ford and allows you to adjust min. idle speed with IAC unpluged. I[/quote]
What difference does the spacer make regarding adjustment?
i don't know how much your engine varies from my 5L. but mine adjusts. How thick is it? Maybe I have one & haven't noticed.

 

the spacer has a couple allen screws to allow air to bypass the iac valve. IMO it is a bandaid for the non cleanable/adjustable throttle bodies, It allows for adjustment of min. idle. Cleaning the throttle body and if need be adjusting the throttle stop achieves the same thing...the spacer does achieve the same thing though..and leaves the teflon so our eggs dont stick