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Truck is running but idling very rough. The idle is searching from 500-1100 and dies.
Checking the TPS signal wire (green ?) I have .96v throttle closed and go to 4.46 at WOT. That is using the battery neg. as my ground point. So that is telling me my TPS is good as I see no dead spots on the meter as I am opening and closing the throttle.
The IAC valve is clean and activating easy on bench test and has voltage when on truck.
I did check the Engine coolant temp sensor and it checks at 36K and some change which is a little low according to specs.
What is next to check to see why the idle is surging cold or hot.
Did not try the second phase of test as truck will not stay running.
Second phase of the test? There is only one part to the KOEO test with two results: active and then stored codes will be displayed. You repair any codes from the KOEO test before performing the KOER test.
It appears that you need to test the air diverter (TAD) solenoid
I have repaired/replaced some of the vacuum lines. Crawling over the rascal yesterday I saw that line that goes into cabin and I believe it was coming from the cruise module. Did not get in cab to see where it goes and check that end of the line. Will check it today and a few other things.
Waiting on the Ford Shop manuals to arrive so I can test the air diverter (TAD) solenoid.
I am trying to get it up and running so I can move it around to do the work I know it needs as time and money will allow. I did not want to drop a ton of money into the rascal until I found out if it would still run. Already got a new rear tank and sender/pump,high pressure pump,tank selector valve in it to see if it would run. The brother in law parked it in 2008 because rear tank was leaking and it has not been started since then. I know it needs new front tank/sender in it and complete front brakes and brake lines (complete) as a starting point to get it road ready.
It appears that you need to test the air diverter (TAD) solenoid
Do you know if both of these solenoids are the same? I see that 1 is available from Ford and the other NLA.
Both solenoids have been removed and their lines that go up to diverter valve plugged into the main vacuum line that feeds the EVR,TAD,TAB. .Great! Nothing better than a shade tree worker. Now to trace all the lines back to there origin and correct everything and try to locate the missing solenoid from Ford or a junk yard.
Last edited by toolman60; May 3, 2022 at 07:35 AM.
Reason: add more information
Well I managed to get it running somewhat today. On cold crankup it still surges bad up/down idle and will die. I notice when it is cold it has a hesitation on quick throttle. I kept it running by holding it between 1.2 & 1.5K after it got hot it ran a lot better and was idling around 750/800rpm and once in awhile it would surge on idle.When you gave it quick throttle it would drop done and search for idle a few times and then level off 750/800 rpm.
I found out the egr valve was stuck open and got it free but also have problem with power to the EGR solenoid or to the EVP sensor. I think I still have an EGR problem as this 1 will not seal tight on the bench. It still lets a little air pass thru .Will do some testing on them tomorrow. Will be heading to pick and pull over weekend to see if I can find the EGR,TAB,TAD solenoids on a car or truck.
Need to see if I can get the Thermactor system back up and running to decide on new exhaust system. I do not have emission testing here so may just eliminate all the emission and place resistors inline for the TAB/TAD solenoids.
I think I got a lifter tap but engine seems to run fine at times so guess it is time to pull intake and check rocker clearance Maybe later down road pull the 6 and rebuild.
Get a piece of thin steel or aluminum and trace out a plate to put between the EGR and the intake, and block it off. An '87 won't show a code, and you won't have to worry about it. Mine's been blocked off since the late '90s or early 2000's. I also put a screw in the main vacuum line going to the solenoid, then put the line back on so it looks like everything is working.
My surging starts about two minutes after a cold start, and stops about 4 minutes later, if the engine doesn't die first. I fixed the dying pretty much by setting my idle between 900 and 1000 rpm. Since I have a NP435 also, the high idle doesn't matter to me, except the famous 4.9 idle stumble is gone at that rpm.
Overly rich will cause an idle surge, check the fuel pressure at the rail. Check that brake booster grommet for cracks and such, mine is clapped out on the '92 which creates a large vacuum leak. This was left for dead with a myriad of vac leaks.
If you have no smog, just grab some of those solenoids and plug them into the harness. The ol' ECU will be happy then. My experience even with low mile AIR stuff is that is does not work anymore with age or works poorly. EGR blocked off will not yield any power gains nor any noticeable loss in economy. Maybe a ping? I have never noticed one. EGR tends to work just fine with age usually.
The rear cat is the restrictive one as I recal, the precat is so-so..unless you have a one cat truck like my pal. I would gut the precat and pop in a high flow unit and some muffler. I am a fan of a Hooker Aerochamber, but I wanted a mandrel bent tailpipe so I went with the Flowmaster kit for these. I like the 70-series Deltaflow unit. Very mild.
Mine will stop the surge if I unplug the water temp sensor, but then I'm stuck in default mode.
Over the years, I've checked every sensor, pressure, followed the post by Broken Wire about fixing the surge, with only a decent improvement. I've learned to live with it. It's only obtrusively present and annoying on a really cold day.
Overly rich will cause an idle surge, check the fuel pressure at the rail. Check that brake booster grommet for cracks and such, mine is clapped out on the '92 which creates a large vacuum leak. This was left for dead with a myriad of vac leaks.
My fuel pressure at rail is 50 KOEO 50 KOER and jumps to about 53 when I hit throttle. No Vacuum leak at booster or anywhere else that I can find with the MightyVac on the tubes an hoses.
Get a piece of thin steel or aluminum and trace out a plate to put between the EGR and the intake, and block it off. An '87 won't show a code, and you won't have to worry about it. Mine's been blocked off since the late '90s or early 2000's. I also put a screw in the main vacuum line going to the solenoid, then put the line back on so it looks like everything is working.
My surging starts about two minutes after a cold start, and stops about 4 minutes later, if the engine doesn't die first. I fixed the dying pretty much by setting my idle between 900 and 1000 rpm. Since I have a NP435 also, the high idle doesn't matter to me, except the famous 4.9 idle stumble is gone at that rpm.
I will give that a try and most likely be doing it permanent with exhaust system replacement. I may be wrong but if it is letting exhaust by at an idle it would not cause the engine to surge. The EGR that is on it now was stuck so I got it free but it does not seal 100% between exhaust an intake. I read that they do not close air tight in 1 thread and do in another so not sure which is correct. Making a block plate will surely tell me if it is leaking by at idle makes it surge in short order.
I do have a new Motorcraft Coolant Temp. Sensor,Engine Temp Sensor,Oil Pressure sensor on way.
Well blocked off EGR and still rough surging idle. Time for my brain to give it a rest for a day or 2 and back at it again.
I am about ready to put the sawzall on the exhaust right after the 2 pipes join as 1 and see if the converter is clogged not letting it breath. Just do not want to hear that loud noise why I am doing rest of work on truck.
