Ford Mustang Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter · #1 ·
Hello, I'm a new member here... Just bought my 1990 white LX 5.0 Hatch 5 spd with only 60k original miles 2 weeks ago. It's in great shape. Interior is near perfect and paint is great.

It has a rough idle, not bad, just a little rough. I gave a full tune up including cap and rotor, plugs and wires. Still idled a little rough. So, I have checked all vacuum lines and have found the one that comes from under the upper intake down to the charcoal cannister probably in need of replacing but don't think there are any leaks...

I turned to the Idle Air Control Valve... Changed that. After changed, I started it up and it was surging up and down and then it'd die. Tried to start and rev but was just surging really bad and die. I even took it out on the freeway and drove it for a bit but every time I took my foot off the gas it would surge and die.
So, my question about this is ... Why would a brand new IAC cause a problem. I put the old IAC back on and went back to being able to run but just a little rough. I did read in another thread that you might have to adjust the Throttle Position Sensor after replacing the IAC? Again, why would a brand new IAC cause a surging problem. I feel like this is my problem because there is no reason why this would happen... I also would disconnect the battery for over 5 mins to clear the computer after I tuned up and after I changed the IAC... just for thought.

Also, wondering about my EGR valve. With the old (working) IAC still on, I unplugged the EGR valve and had no change in the motor. I can see the pump moving back and forth as I rev it up... But not sure if by unplugging I would see any difference in the motor. I did notice the plug connector clip part on the EGR was broken off which leads me to wonder about this EGR... Did someone change it in the past and broke the clip off???

Thanks Guys

Jimmy
 

·
Registered
Joined
·
161 Posts
Could be the iac you bought is bad. the egr put vac to it at an idle and you should see a change. It doesn' t do anything at an idle. It could be stuck open a little.
With it idling with the old iac disconnect the wire to it and see if the idle changes.

Ken
 

·
Registered
Joined
·
382 Posts
Best thing to do is to buy a code reader and check your codes first, then you will know where to start looking. might save you some money in the long run :bigthumbsup and make sure the iac you bought is a motorcraft I have had bad experences with the other brands and when you change it out disconect your battery for about20 mins. to reset the computer, or it could take a couple of days for you to notice a change,eventually the computer will reset itself just takes longer
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #5 ·
Wow, thanks for the respnses... Just got done watching Jeff Gordon win FINALLY!

Ok, I have no check engine light but when I unplug the EGR the light comes on...

With the old IAC, I unplug it and the motor dies. So, I'm guessing that it is working...

What next? Where would you guys recommend buying a code reader? I own an OBD II reader but that won't work with these stangs right?
 

·
Registered
Joined
·
161 Posts
You dont need a code reader yet. and autozone,advance and others will read it for free.
Yes your iac is working . and yes the light will come on if yopu unplug the wires.
Remove the egr and look for the pintle to have something stuck in it .
Put a vac line on the egr and apply vac. does the diaphragm move? does it hold vacuume?
the pintle should be closed and sealed with no vac applied.


Ken
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #7 ·
You dont need a code reader yet. and autozone,advance and others will read it for free.
Yes your iac is working . and yes the light will come on if yopu unplug the wires.
Remove the egr and look for the pintle to have something stuck in it .
Put a vac line on the egr and apply vac. does the diaphragm move? does it hold vacuume?
the pintle should be closed and sealed with no vac applied.


Ken
I will check the EGR, I did see it move at the end of each rev I gave the motor by hand... When you say apply vac by putting a vacuum line on it, what exactly do you mean? What vacuum line? One from the car or an actual vacuum cleaner line? ( I know that's a dumb question)

Is there anything else on these cars that would cause a rough idle besides vacuum, egr, iac, plugs, wires, cap, rotor?


On a side note, does anyone ever remove the motor pull tabs that are bolted to the sides of the heads? They are annoying me and I want to remove them but don't want to mess something up... I think they are double bolted to the headers.
 

·
Registered
Joined
·
297 Posts
I will check the EGR, I did see it move at the end of each rev I gave the motor by hand... When you say apply vac by putting a vacuum line on it, what exactly do you mean? What vacuum line? One from the car or an actual vacuum cleaner line? ( I know that's a dumb question)

Is there anything else on these cars that would cause a rough idle besides vacuum, egr, iac, plugs, wires, cap, rotor?


On a side note, does anyone ever remove the motor pull tabs that are bolted to the sides of the heads? They are annoying me and I want to remove them but don't want to mess something up... I think they are double bolted to the headers.
apply vacuum or suck on the egr hose to see if the car idles down or trys to stumble,


and the Motor pull tabs can be removed just save them, i took them off when i put headers on much cleaner ;]
 

·
Registered
Joined
·
16 Posts
Discussion Starter · #9 ·
apply vacuum or suck on the egr hose to see if the car idles down or trys to stumble,


and the Motor pull tabs can be removed just save them, i took them off when i put headers on much cleaner ;]
cool thanks... Those tabs are soo ugly and just wasn't sure if I would loosen the header by taking them off.
 

·
Registered
Joined
·
13,166 Posts
Egr will throw a CEL when bad. Its one of only a few things that will. IAC can become dirty which could cuase less air in the engine at idle. Could be the new one is letting in more air which isnt allowing it to run. Check the green (+) and black (-) wire for .77-.99v on the tps
 

·
Registered
Joined
·
897 Posts

·
Registered
Joined
·
382 Posts
1 - 12 of 12 Posts
Top