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Discussion Starter · #1 ·
Hey everyone. Recently my 95 3.0 Taurus has had a hunting idle at startup. By hunting I mean, revs up and down constantly. It does it for about 2 minutes, then comes out of it. It seems that it is when the engine is cold, (granted its been very hot and humid here) and has sat over night. If it sits for 4 hours or so, no issue. It also seems that sometimes once I put the car in gear, it becomes less of a hunting idle, to sometimes normal idle (for my car).

I am planning to do a full tune up before winter gets here, but wanted to get some ideas of things I should also look at. It seems my car has always had a slightly erratic idle. Never really idles smoothly, especially while in gear with the brake on.

I have also noticed that when I start the car and drive, it get a hesitation, for lack of a better term, for a short time when I press the gas. It doesn't do it once the motor has been running for 10 minutes or so. The best way I can describe it, it almost feels like a dead spot on a carb'd vehicle.

I plan to do plugs, check/replace plug wires, fuel filter, and possibly a few sensors. Just not sure which ones sound like they could be the culprit. At first I was thinking coolant temp sensor, since it does it on cold starts. I am not getting and gauge fluctuations though. Some say you would see incorrect coolant temp gauge readings if temp sensor is bad.

For the dead spot feel, I am leaning towards throttle position sensor, but seems odd that it only does it when the engine is not warmed up.

If the sensors are cheap, I would probably just swap a bunch of possible culprits out.

Thoughts or ideas?

Also, noticed my rear valve cover gasket is leaking. It looks like a pain to get to. I haven't stared at it for very long, but it looks like I will need to pull the throttle body at the very minimum to change it out. I don't need to pull the intake manifold as well do I?

Does anyone have any tips or tricks on rear valve cover replacement on the 3.0?

I want to get it fixed before the cold weather gets here. I have been putting it off for a while now cause its been so hot and humid here. But realize chasing down a problem can take several weeks, so figured I would get started now. LOL.

Thanks for any input.

Shawn
 

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Hey everyone. Recently my 95 3.0 Taurus has had a hunting idle at startup. By hunting I mean, revs up and down constantly. It does it for about 2 minutes, then comes out of it. It seems that it is when the engine is cold, (granted its been very hot and humid here) and has sat over night. If it sits for 4 hours or so, no issue. It also seems that sometimes once I put the car in gear, it becomes less of a hunting idle, to sometimes normal idle (for my car).

I am planning to do a full tune up before winter gets here, but wanted to get some ideas of things I should also look at. It seems my car has always had a slightly erratic idle. Never really idles smoothly, especially while in gear with the brake on.

I have also noticed that when I start the car and drive, it get a hesitation, for lack of a better term, for a short time when I press the gas. It doesn't do it once the motor has been running for 10 minutes or so. The best way I can describe it, it almost feels like a dead spot on a carb'd vehicle.

I plan to do plugs, check/replace plug wires, fuel filter, and possibly a few sensors. Just not sure which ones sound like they could be the culprit. At first I was thinking coolant temp sensor, since it does it on cold starts. I am not getting and gauge fluctuations though. Some say you would see incorrect coolant temp gauge readings if temp sensor is bad.

For the dead spot feel, I am leaning towards throttle position sensor, but seems odd that it only does it when the engine is not warmed up.

If the sensors are cheap, I would probably just swap a bunch of possible culprits out.

Thoughts or ideas?

Also, noticed my rear valve cover gasket is leaking. It looks like a pain to get to. I haven't stared at it for very long, but it looks like I will need to pull the throttle body at the very minimum to change it out. I don't need to pull the intake manifold as well do I?

Does anyone have any tips or tricks on rear valve cover replacement on the 3.0?

I want to get it fixed before the cold weather gets here. I have been putting it off for a while now cause its been so hot and humid here. But realize chasing down a problem can take several weeks, so figured I would get started now. LOL.

Thanks for any input.

Shawn
Loping idle and sluggish response of cold startup sounds like leaking intake gaskets to me. After 15 years it's time. I would plan on pulling upper and lower intake manifolds, doings your intake gaskets, valve cover gaskets, and replacing all the PCV hoses at the same time. Also clean the intake and all EGR passages and tubes. Do it all at once and save yourself some trouble.

One thing people don't get about the PCV system is that it vents positive pressure from the crankcase. If a vent hose rots and collapses from intake vacuum, you them have excessive pressure throughout the crankcase that causes lots of mysterious oil leaks.
 

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Discussion Starter · #3 ·
Loping idle and sluggish response of cold startup sounds like leaking intake gaskets to me. After 15 years it's time. I would plan on pulling upper and lower intake manifolds, doings your intake gaskets, valve cover gaskets, and replacing all the PCV hoses at the same time. Also clean the intake and all EGR passages and tubes. Do it all at once and save yourself some trouble.

One thing people don't get about the PCV system is that it vents positive pressure from the crankcase. If a vent hose rots and collapses from intake vacuum, you them have excessive pressure throughout the crankcase that causes lots of mysterious oil leaks.
It does lope like a vacuum leak, but doesn't do it all the time. I can understand that when the engine gets warm gaskets can re-seat, but didn't think my issue was that serious.

Would there be other systems that would be caused by an intake leak? I would like some other things to check to help determine if that is the issue.

Thanks

Shawn
 

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Some say you would see incorrect coolant temp gauge readings if temp sensor is bad.

I believe there are separate sensors for temp gauge and temp signal to PCM on a G2.
 

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Discussion Starter · #5 ·
Some say you would see incorrect coolant temp gauge readings if temp sensor is bad.

I believe there are separate sensors for temp gauge and temp signal to PCM on a G2.
Good info. They are cheap enough, I will probably just throw one in to make sure.

Thanks

Shawn
 

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Discussion Starter · #6 ·
Well after doing more research, it seems it can be a bunch of different stuff. So my plan is to do a big tune up on it.

Can you look over my list and let me know if I am missing something, or something else I should consider?

I plan to do plugs, wires, cap, rotor, coil, throttle position sensor, coolant temp sensor, idle air valve, fuel filter, intake air temp sensor, pcv, and check over all the vacuum lines.

Since I have to pull the upper intake manifold (throttle body) to get to the rear valve cover, I am just going to do upper and lower intake gaskets. Reading in the Chilton manual, it says you need to pull the number 3 pushrod when pulling the intake manifold. Why is that? Also does anyone know what size torx bit is needed?

I am debating on replacing the EGR valve as well. Am I correct that there are also 2 sensors that work with the EGR valve? If so, should they be replaced as well?

I know its a little overboard, but from what I can tell, everything is OEM still and I am getting ready to turn 180K. So figured it can't hurt to take a bunch of possible issues out in one swoop.

Thanks

Shawn
 

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You are planning to waste a huge amt of $$ on parts the engine likely does not need. For example, you can read ECT voltage at operating temp by back probing the connector and see if the value is correct. TPS can be tested while opening / closing throttle KOEO and making sure closed throttle volts is in spec and no jumps / dropouts as throttle opened. IAC rarely causes the problems you are having. I suggest cap, rotor, wires, plugs and intake gaskets as at start.
 

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I'm with Jeff, don't throw a bunch of sensors on it. I can't describe the awful feeling of throwing away good old parts and replacing them with defective new parts. If it ain't broke, it's often better than the aftermarket electronics.

Remember to replace all soft/rotted PCV hoses and elbows and clean out all the EGR passages.
 

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Discussion Starter · #9 ·
You are planning to waste a huge amt of $$ on parts the engine likely does not need. For example, you can read ECT voltage at operating temp by back probing the connector and see if the value is correct. TPS can be tested while opening / closing throttle KOEO and making sure closed throttle volts is in spec and no jumps / dropouts as throttle opened. IAC rarely causes the problems you are having. I suggest cap, rotor, wires, plugs and intake gaskets as at start.
Well the valve covers have to get done. So the upper intake gasket would have to be replaced anyways. Are you saying to do both upper and lower intake gaskets?

Also, where can I find specs on TPS and coolant temp sensor ranges? I have a Chilton, but it doesn't go much into detail on testing. Mainly removal and installation steps. Unless I am looking in the wrong spot. Is the TPS based on a 0 to 5 volt range like many other cars?

Also, you believe the IAC would not be a possible cause of my issue. Could you please explain a bit more? Besides the hunting idle at startup, I do have a very choppy idle all the time. It gets worse when I run the A/C. Its enough that if I am sitting at a stop light for a length of time, it will feel as if its gonna die. It hasn't died on me yet, but just gets a real choppy feeling. I always thought that was a tell tale sign of a dirty or bad IAC.

I'm with Jeff, don't throw a bunch of sensors on it. I can't describe the awful feeling of throwing away good old parts and replacing them with defective new parts. If it ain't broke, it's often better than the aftermarket electronics.

Remember to replace all soft/rotted PCV hoses and elbows and clean out all the EGR passages.
I can understand where you are coming from. Its just I don't have alot of experience with these motors to go through and trouble shoot issues. And I don't have alot of time as well. That is why I was thinking of just throwing new parts on it.

But if I can get some specs as to what sensors should be reading, I can test them to out to see if there is an issue.

I appreciate the input.

Thanks

Shawn
 

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IAC failure usually results in constant low idle or constant idle, not rough idle near the target idle speed. One test for IAC is to tap on it with a wrench / hammer when idle is acting goofy and see if IAC makes any difference.

Sensor transfer functions (voltage output for a given temp) are all over the web.... search. Ford has used the exact same transfer functions for most sensors like ECT across most model lines (diesel not included) for 25 years.

Yes, I am suggesting doing both the upper and lower intake gaskets.
 

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Discussion Starter · #11 ·
I managed to find some spec ranges for the coolant temp and IAT sensors. They use the same measurements to give a given temperature.

From what I can find, TPS is ranging from 1 volt up to 4.5 or 5 volts at WOT.

Going to do some testing tomorrow and see what I can find.

Thanks

Shawn
 

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Discussion Starter · #12 ·
Figured I would give a bit of an update, if you want to call it that. LOL.

Took the car into a local shop since I could find nothing wrong. And of course it wouldn't do the surging idle at startup. But it has cooled off here and I haven't experienced it again. But still getting the take off hesitation when the engine is cold.

The other problem I was having was when I was sitting at a light, I would get a stumble in the idle. The car would shake as if it was going to die, but never actually would die. Its not a constant thing either. Stop at one light, get a stumble, next light, idle fine, etc. Slide it up into neutral and it would idle fine. So it was only with a load on the engine.

The shop checked short term fuel trim and found no issues. He said he was not able to check the long term fuel trim because either his machine or the car would not give that info.

But if you sit with the car in gear and foot on the brake, every so often you can feel the idle stumble a bit. It seems as the longer you sit there, the worse it gets.

The shop was at a loss. Said they couldn't find any issues.

Shawn
 

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I would do as Jeff K suggested when idle is surging in park. Set e-brk. Get out and tap iac with handle end of screwdriver. If idle improves, remove and clean iac with tb clnr. or replace. Might also search for rough idle thread by tonyroc14. Good luck.
 

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Discussion Starter · #15 ·
I would do as Jeff K suggested when idle is surging in park. Set e-brk. Get out and tap iac with handle end of screwdriver. If idle improves, remove and clean iac with tb clnr. or replace. Might also search for rough idle thread by tonyroc14. Good luck.
Yeah I looked at that thread before I posted my update. His turned out to be a vacuum leak. I have tried the tapping on the IACV and got the same results he got. I will try to unplug the IACV next time it happens and see if the car dies. Is that a good way to check for a vacuum leak somewhere?

The shop said they checked all the hoses and couldn't find any leaks. Said they used some propane as well to see if they could just not physically see a cracked hose.

And he said the short term fuel trims look right on spec, which (he claims) if there was a vacuum leak, you would see it in the short term fuel trims.

Thanks

Shawn
 

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You can not see short term fuel trims with EEC IV. You can, using a breakout box or backprobing the connector, measure O2 output voltage, which switches rapidly rich lean. O2 votlage is related to STFT, but is NOT STFT. I am assuming your 95 isnt one of the few hundred that came with OBDII / EEC V.
 

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Discussion Starter · #18 ·
sounds like a vacuum leak. Same thing happened to me, just fixed it.
It could very well be, but so far, everything I have tired, as well as the shop have not yielded the culprit.

You can not see short term fuel trims with EEC IV. You can, using a breakout box or backprobing the connector, measure O2 output voltage, which switches rapidly rich lean. O2 votlage is related to STFT, but is NOT STFT. I am assuming your 95 isnt one of the few hundred that came with OBDII / EEC V.
No, mine is OBDI. Is there another way to check for vacuum leaks besides those that I and the shop have already tried?

Usually I can find them with some carb cleaner or propane, but so far that has not shown any areas of a possible leak.

Shawn
 
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