TCCoA Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 · (Edited)
So I got picked up a 94 Thunderbird LX, 4.6. Car runs and drives like a champ other than one minor inconvenience...

When I cold start it, the engine will start, the RPM will jump to around a grand, then drop straight down to 0 and die. I have to keep my foot on the gas and hold the idle at 550/1000 rpm for about 60 seconds, then the engine will hold its idles and work fine. Once its warm, its not an issue. Only happens on cold starts. I live in Michigan, its getting cold outside. The colder it is, the longer I have to hold it.

Car came from a trusted friend. Fresh Oil, New Plugs, and wires.

I read that it could be a dirty IAC. So I pop the hood and and first thing I see is the top of the MAF was missing, i dont know if those things are filled with goo, but there is a layer of clear gel over the electrical components. ( I assume was put there when the maf was molested.)

I purchased a new MAF from Rock auto (i know.... )
Installed it, car ran worse.

I located the IAC, and one bolt was half way backed out! I pulled it and its clean as a whistle. No bind ups in the spring mechanism. Also ohmed out at 9.7 ohms

I cut a new gasket, cleaned the mating service and re-installed it.

Car runs like ****. Wont even stay running.

Put the old one back on, car fires right up but original issue remains!

When I changed the MAF, I unhooked the battery for 10/15 minutes. Made no difference.

Tried unplugging MAF, letting car idle for 5 seconds, Power off, re-connect. Made no difference.

Do I need to remap the EEC when changing a MAF?

Is it because its from rock auto?

Is there anything else I can check??


Super appreciate any help or suggestions! Thanks in advance for the help!
 

·
Super Moderator
1997 Thunderbird 4.6, 1998 Mark VIII LSC
Joined
·
10,237 Posts
Yes, you'll need to do a KAM reset after replacing the MAF. The fuel trims in memory and ISC integrator are all distorted due to O2 feedback from the skewed MAF transfer function, so see what happens after leaving the battery disconnected for a few minutes.

Besides that, it really sounds to me like the IAC is misbehaving still (cleaning and resistance checks do not always guarantee proper functionality unless you've transplanted it to a different car and all was well).
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #3 ·
Yes, you'll need to do a KAM reset after replacing the MAF. The fuel trims in memory and ISC integrator are all distorted due to O2 feedback from the skewed MAF transfer function, so see what happens after leaving the battery disconnected for a few minutes.

Besides that, it really sounds to me like the IAC is misbehaving still (cleaning and resistance checks do not always guarantee proper functionality unless you've transplanted it to a different car and all was well).
Thank you for the input, I just googled KAM reset and it says to disconnect the negative battery terminal for 5 or so minutes.

That leads me to believe that I did it wrong by completely disconnecting the battery (positive and negative) when i disconnected it, i left it for about 15 minutes. Maybe I should just disconnect the negative terminal for 5 minutes, and if I can get it to start, drive it around the block a few times so the computer can learn the new numbers?
 

·
Super Moderator
Joined
·
7,951 Posts
It doesn’t matter how you disconnect the battery. What you did should have cleared the KAM just the same as disconnecting only the negative terminal. My advice at this point is to get a motorcraft IAC and MAF for the car, since both of those are suspect, and go over the whole top end of the engine looking for vacuum leaks.
 

·
Registered
96 TBird, PI cams, FRRP intake, Magnaflo exhaust, added weight (stereo)
Joined
·
63 Posts
Vacuum leaks at the intake manifold could be a cause. Those tend to get better once everything heats up.
 

·
Premium Member
Joined
·
321 Posts
Update?

Sounds like an easy fix, manually maintain idle until it warms up. Yeah my '95 did that for a while long time ago. Never fixed it but is stopped doing it. Maybe in conjunction with something else I fixed.

What about something simple like the PCV valve? If it's stuck open it the engine will lose vacuum. Maybe the vacuum to the EGR valve? Again, if the EGR valve is stuck open when cold it will idle poorly and could stall.

It's nice when someone says yeah the exact thing happened to me and this is how I fixed it and you try it and it works. But expect having an old car will be an exercise in research and logic if you are doing your own repairs/upgrades.

Might want to treat yourself to a cheap scan tool to check fuel trims and the like that can steer you to the fault.

Good luck and enjoy solving the problem.

Jim
 

·
SuperNewbie
1995 Thunderbird LX 4.6 red
Joined
·
3,146 Posts
There have already been plenty of good suggestions. Keep in mind that just because the IAC is clean, that doesn't mean it is good.
 
  • Like
Reactions: Trunk Monkey
1 - 7 of 7 Posts
Top