Idle and cruise control probs

[qazvick]

Hey guys I'm sort of a noob with these cars. I used to have a '76 Marquis Brougham and I Just bought an '87 Crown Vic Country Squire. I got a couple probs.

1. When I bought the car, it idled great. The first night I got her I took it out and ran the :guns: shit out of it. But it never overheated. But since then, it doesn't like to idle in OR out of gear. The idle control screw is all the way in. I've cleaned out the TPS and IAC. I've cleaned the contacts on the distributor. Plugs look fine. What else should I do?

2. The cruise control will engage, but when it does, all it does is floor the gas pedal and never lets off. I let it take me all the way up to 80mph till I hit the brakes. Any ideas?

Thanks for any help guys.

[Blaze86Vic]

The VSS on the back of the transmission may not have a good connection somewhere. If it doesn't then the current flowing from it when it is activated will decrease as the weak connection heats up. This is interpretad by the cruise module to mean that the vehicle is slowing down, so it adds more gas to compensate. If all the wiring is good then your cruise module could be bad. Get a junk one out of another car and see if that fixes it.

As for the idle, how does it not like to idle? I'm assuming that it idles too high since

The idle control screw is all the way in.

.
This problem stands a good chance of being a result of a bad idle air controle valve. The one on my engine has failed once. When it failed it would set the idle in nuetral at 3000rpm!! Even though my engine is quite a bit different from yours, I think the idle air controle valve is the same design.

[qazvick]

The idle is a horrible idle when it does. But 95% of the time it stalls cause the idle is tooooo low. However, the screw is maxed in.

Also another thing... When I'm cruising down the road at any speed. If I hold it at that speed, it stumbles and hesitates like crazy untill I add the SLIGHTEST bit of acceleration and then it goes smooth again. Hope that helps.

And what's VSS stand for?

[Blaze86Vic]

VSS (Vehicle Speed Sensor)

If the screw is all the way in then you are getting less air at idle, turn the screw all the way out and see what it does. (don't unscrew it to the point that it falls out) I could be wrong but I don't think so, I'm pretty sure thats how it works on all cars. I say this because I never messed with much on my factory engine. So most of what I know is what I've learned from the engine setup I have now.

Second, your cruising speed stumbles could also be a result of the idle air controle valve (IACV) and/or the screw being all the way closed. And its stands a good chance that it is, because it screws up when your idle air is the primary sorce of intake.

[roastdawgg]

FYI the TPS cannot be cleaned...it is an FRU (Field Replaceable Unit)...it can be calibrated though.

[gadget73]

VSS for the cruise for sure, but you might also want to check the TPS (throttle position sensor) for the idle problem and the hesitation. Check the voltage on the green wire. At idle it should be .95-1.0v and should smoothly increase to about 5v at WOT. Do this with the engine not running of course. Idle screw should be only run in enough to open the throttle plate a little bit so it doesn't stick.

[qazvick]

I know for a fact that the screw is all the way in, and that the farther in the screw goes, the more open the butterfly is.

It seems that the IAC keeps popping up. Is it worth my time to go find one at a junk yard or should I drop the $50 for a new one? What about the TPS? I'll check the voltage on it.

Thanks for all the help guys.[/quote]

[qazvick]

tps voltages

idle = 1.23V
WOT = 4.87 V

good or bad?

[gadget73]

WOT is fine, idle is high because the screw is cranked way in. Mostly what you need to look for is a smooth change in voltage as the throttle is opened. If the IAC has been cleaned and the idle is still super low, its probably shot and needs replacing. Try tapping it on the side to see if its just stuck, or spray some penetrating oil in there to see if it'll free up and start moving, but it sounds like you may be needing a new one. Might also not be a bad idea to check the fuel pressure. Should be 35-45 psi.

[TommyN]

TPS at idle should be under 1V, around .90 - .95V. Adjusting the throttle set screw so the plate is further open than stock will raise the value. Playing with the throttle set screw is not really recommended, but now that you have moved it it would be a good idea to set it right.

The idea is to have the set screw adjusted just a bit so that the throttle plate does not touch the wall of the throttle body. Basically back off the screw until it does touch and then turn the screw to move the throttle butterfly off the wall, about 1/2 turn.

Maybe unbolt the IAC and clean it out. It could be carboned up.

Tom

[qazvick]

Ok well before I even got the car the idle screw was all the way in. I did unscrew it as far as it would go with the spring on the screw still having some pressure on it, but the lowest I could get the voltage to go was 1.07. It still ran the same way. Crappy cruise, hardly any idle, nothing changed. I did remove the IAC and cleaned it with carb cleaner, also cleaned along where the air enters the TB.

I'm still wondering if it's worth a shot at the junkyard for another IAC (cause there are 2390482908342 of these things out there)

[TommyN]

Your TPS might be bad if you had the idle screw backed all the way off and it was still 1.07V.

A junkyard throttle body might be something to try if you can get it cheap enough.

If you want to get that TPS under 1.0 volts, you can unbolt it, drill the holes in it oversized, then reinstall. Now you will be able to loosen the screws, and twist the TPS to get it to idle .90 - .95 volts.

You can tell when the screw is backed off far enough because it won't be touching the lever at the bottom of the throttle body. Maybe back it off so it is not touching, get it to barely touch it, then give it 1/2 turn more.

Tom

[qazvick]

"A junkyard throttle body might be something to try if you can get it cheap enough. "

Are you saying I need a whole new TB?

"If you want to get that TPS under 1.0 volts, you can unbolt it, drill the holes in it oversized, then reinstall. Now you will be able to loosen the screws, and twist the TPS to get it to idle .90 - .95 volts. "

You mean so I can "pivot" the tps and adjust it like that? I'll try that out tomorrow and see what happens. SOUNDS BETTER than spending $30 on a new one haha.

But it still sounds like I need a new IAC too right?

[TommyN]

A junkyard throttle body would likely come with a TPS and IAC and might cost the same as an IAC.

Why not get the TPS adjusted first, then see how it idles. Not sure your IAC needs replacement.

Tom

[qazvick]

Alright I'll do the tps adjustment tomorrow and get back to ya. Thanks for the help tonight guys