Garbage idle

[91waggin]

It started like this: Originally, when I started my car, it would fire and then immediately stall, and only if I immediately put it into gear would it continue to run. The last time this happened to me it turned out to be a vacuum leak. So I did a little investigating, and sure enough, the PCV Grommet with the valve in it had worked its way out of the block. Fixed that, and now we have this:

Whenever I start the car and the motor's cold, it will rev up to ~1200, and then act like it wants to die, and at about ~200 rpm, it will catch itself and rev back up to ~1200, and then the cycle will repeat itself. When in gear, it will move back and forth between 500 and 800 rpm, resulting in the car pulling against the brakes when I sit at a stoplight. Once you get rolling, above 1000 rpm or so, it runs and pulls just fine.

I have taken the propane torch and waved it all over the entire engine bay, trying to find more vacuum leaks, to no avail. I also got code 34, but that was the only one.

Here's what I've done so far:

• New IAC
• New TPS
• Inspected EGR valve, and it appeared to operate properly when I applied vacuum with a hand pump
• Replaced EGR vacuum solenoid, since it didn't pass the test outlined in the Chilton's manual.

Wires, cap, and rotor are all about 6-8months old. Plugs are about two years old.

Air injection system is disconnected, with a wicked exhaust leak coming out the tube from the back of the head. No idea why I didn't get codes for that system, but maybe it's because the solenoids are still there, but the vacuum side is capped.

Any thoughts?

[gadget73]

That still sounds like vacuum leak problems to me. 34 can be caused by leaks in the red plastic tubing between the manifold and the smog solenoids, particularly at the connector. Might want to look at that.

Bad temperature sensors can do this too. Might want to dig out the voltmeter and check them. Fordfuelinjection.com has a section with sensors, and charts showing the resistance at a given temperature. If the ACT or ECT are out of range, it causes problems.

[91waggin]

That still sounds like vacuum leak problems to me. 34 can be caused by leaks in the red plastic tubing between the manifold and the smog solenoids, particularly at the connector. Might want to look at that.

Bad temperature sensors can do this too. Might want to dig out the voltmeter and check them. Fordfuelinjection.com has a section with sensors, and charts showing the resistance at a given temperature. If the ACT or ECT are out of range, it causes problems.

Goofy. I pointed my propane torch right at both ends of that red plastic line and everywhere in between and nothing happened.

I will check ACT and ECT. You'd think they would throw codes though, wouldn't you?

Thanks!

[gadget73]

maybe, maybe not. They only throw codes if they are out of the sane range. They can produce a reading not outside the ECM's realm of acceptable values, but still give the wrong value though.

[91waggin]

hmmmmm....both sensors are more than likely original so I'll just replace them.

[86VickyLX]

When you replaced the TPS, did you disconnect the battery for the computer to relearn?

[91waggin]

yes. I disconnect the battery before I install any engine sensor

[ironstealth]

mine was doing the same thing. turns out that the idle screw was so far backed out that the throttle plate was actually closed,and AIC was working overtime to keep the car running. You will have to re-adjust the tps to the new idle setting.
If it is idling, unplug your AIC.(do this on a "no load" condition as anything like lights,stereo,blower fan,etc) if your car dies immediately,your idle isnt even set correctly. This is where a tach is gunna help. A haynes manual(or equivelant) is a bit more specific on the idle setting,with using a feeler gauge on the screw and throttle stop and such.

[gadget73]

I'm too cheap to just hang sensors on. I test them first. If they test OK, spending money for new ones will only make your wallet lighter.

[91waggin]

mine was doing the same thing. turns out that the idle screw was so far backed out that the throttle plate was actually closed,and AIC was working overtime to keep the car running. You will have to re-adjust the tps to the new idle setting.
If it is idling, unplug your AIC.(do this on a "no load" condition as anything like lights,stereo,blower fan,etc) if your car dies immediately,your idle isnt even set correctly. This is where a tach is gunna help. A haynes manual(or equivelant) is a bit more specific on the idle setting,with using a feeler gauge on the screw and throttle stop and such.

#1: TPS on this particular 5.0 isn't adjustable.
#2: Throttle screw has the plate just cracked. I have a tach. Before this goofiness started, I had that screw adjusted properly. It was idling at ~650rpm in gear.
#3: I thought that the car was supposed to die if you unplug the IAC. If it doesn't, it just shows that the IAC isn't doing anything and has no control over the idle.

---------------------
UPDATE:
I checked the ACT and ECT sensors. Both check out just fine. I have pulled the upper intake, and am proceeding to inspect every fucking vacuum hose I can lay my hands on, both visually and with my hand vacuum pump.

More info later.

[ironstealth]

the IAC is only supposed to help on cruising,electrical load,steering load(one test procedure to check is if you turn the wheel lock to lock,and if the Iac cannot adjust quick enough or not at all,it could be bad) and slowing the vehicle down. The motor is supposed to idle on its own without the help of the IAC. Thats why you unplug it while idleing,set the idle, and plug it back in. Slightly elongating the tps screw holes can give a small amount of adjustability. Ofcourse the idle has to be set correctly before you set the tps. Lets say for instance my plate was closed like before and i set the tps to that setting. When i reset the idle,the tps can now be slightly out of range. And it was. Set it to .98 volts on idle4.8-4.9 wot,koeo by loosening the screws and twisting the tps to the correct setting. I think there is even a sticky on this....

[91waggin]

Well, spent the entire fucking day messing with this thing, and I get it put back together and now it won't run at all. I start it, it'll fire and rev to ~1500, and then die. Even if I open the throttle halfway it'll only get me a second or two of run time before it stalls again.

I removed all the plastic vacuum line on this thing. Completely removed the vacuum harness having to do with the air injection system. Of the three vacuum spots on the back of the upper intake, I have one going to the EGR solenoid, one going to the FPR, and one going to the vacuum tree on the firewall. Then I have a vacuum line going to the MAP, another going to PCV, and one going to EVAP purge solenoid.

I replaced these hoses:

• Intake to EGR solenoid
• Intake to FPR
• Intake to MAP
• Intake to EVAP purge
• Intake to PCV

I hooked my handheld vacuum pump up to the line going to the vacuum tree, and there was no leakage at all. Held the vacuum and when I came back five minutes later it was still holding vacuum.

Replaced the upper to lower intake gasket and fuel filter.

Throttle plate is cracked open with the screw, IAC is connected.

Maybe TFI module? Is there a way to test the TFI module?

[Leo]

my brother had the same problem with his 90 cv 5.0. the car would start then die. if it did start it would run like shit. it turned out that the fuel pump was bad. when he got it fixed, it solved the problem.

[ironstealth]

fuel pump could have sucked something up(screen came loose maybe),could be worn out too. its worth a shot,as if you cant get a constant voltage to the pump,it cant properly operate. My bros 5.0 had a craked selonoid(right next to the battery)and it did this. any new codes? might not be able to get running long enough to let the comp figure out whats going on. Possibility that the inertia switch could be faulty. theres a code for that too. LUK mang

[gadget73]

Check the fuel pressure, much more reliable than checking for fuel pump related codes. The code that will show up is secondary fuel system failure, which just means the ECM sees no power on the pump side of the fuel pump relay. If the pump is shot, but has power it will set no code.

Have you hooked a voltmeter to the TPS to verify that the idle position voltage is somewhere between .8 and 1.2v ? Thats the accepted OK range for idle. Its not really adjustable, but if its outside that range it will cause you all sorts of stupid problems. Stuck shut IAC can cause this too, but you should be able to keep it running with a bit of throttle. Bad EGR spacer gasket between the spacer and upper intake could do this too, if its sucking exhaust fumes through the failed gasket it will run pretty horrible.