Surging idle when cold

[junkyardjeff]

When cold the idle will surge on my 88 bronco with a 5.0 for a minute or until I put it in gear,the fuel pressure is on the low side of the range and everything is new and not setting any codes. new plugs got it starting on the first try but I need to find out the surging issue and what should I check.

[wayne petty]

http://i.imgur.com/WMDprhm.jpg first.

second.. circuit tester shoved into the positive side of the coil primary connector..  slowly turn the key on..  crank the engine and return to run.. then slowly off.. this checks the IGN1 circuit off the ignition switch..

third..   circuit tester into the red wire at the idle air control solenoid.  same key operation.. off, ON, Cranking.. ON.. off.  you should have nice bright test light without any drop outs.. this checks the EECIV main relay output..

forth..   engine running..  if you can get at the wires to the inertia switch.. perform a voltage drop test across them. meter set to 20 volts DC first then at 2 volts DC.. less than 0.04 volts is great.. this checks the condition of the electrical contacts in the inertia switch.. they do fail..

forth part 2.. if you have a really long test lead.. hook one up to the positive battery and the other to the either of the inertia switch wires.. i would think that less than 0.1 volts 1/10th of a volt would be good.    why this test.. on some other similar vintage fords.. i have found electrical supply issues to the fuel pump relay.. the fuel pump and main relay contacts are supplied most of the time on different  fusible links and circuits from the starter solenoid connection..

forth part 3...   digital volt meter set to 10 AMPS DC or greater.. some have 15 or 20 amp DC settings..  unplug the inertia switch..  hook the meter leads to the inertia switch terminals so the amp meter shunt is in the circuit.. start the engine and monitor the amp draw.. i like to see less than 7 amps of draw.. it should also be stable..  there is a wire you can ground at the EECIV test connector that will turn on the fuel pump relay to do this without the engine running..   you are now monitoring fuel pump amp draw..

i am taking you have performed the KOEO and KOER tests..

inspected the computer circuit board for cracked solder joints..

verified that the ground connections next to the computer are 2 black wires from the harness and the braided ground strap from the back of the engine..  are mounted to the firewall by the green double ended stud..   only the ECM harness support tab goes on the upper side with a single nut holding that on.

this is just the normal stuff i do daily with almost any EECIII, EECIV, EECV OBD2 ford..  same test procedures until it gets to the return less systems that use a fuel pump driver module..  these tests also work great with versions that use the CCRM.. black box with relays in it up near the radiator.

[junkyardjeff]

I will do the tests after work and see what I get.

[crdnblu]

An additional consideration:

http://www.muscularmustangs.com/iac.php

[junkyardjeff]

I will try cleaning the IAC and now its idling normal.

[junkyardjeff]

I have not had the time to do the test yet but have noticed when very cold no surge but wants to surge when the motor is a little warm.

[crdnblu]

A bit confusing: "I will try cleaning the IAC and now its idling normal."  Have you had a chance to check the IAC?  If not, the normal idle when cold, but surging when warm, could still point to the IAC.  The internal plunger is sometimes prone to sticking, not moving through its full range.

[junkyardjeff]

I have not had time to check it and will clean it when I get off the computer,been more worried about changing the trans fluid to keep me from removing it again.

[Arnold]

I have not had time to check it and will clean it when I get off the computer,been more worried about changing the trans fluid to keep me from removing it again.

  I would flush it with Seafoam Trans Tune. My .02
  I have good luck doing that.

[junkyardjeff]

Put another IAC that I think originally came off the throttle body that is on the truck and will see how it does and I did clean it.