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Discussion Starter · #1 ·
I have a 98 Taurus Se 3.0 OHV engine. Code "U" When I start the car up when its cold, the idle surges high/low. It does get better when it warms up. It surges so bad that when you hold on the brakes, it literally make the car jump/hop. I have replaced the IAC Valve and this made no difference. I have tried to find a vacumm leak, but cannot. Not saying there isn't one, just I haven't found any. Could someone please give me some great advice for this. I have read about intake gaskets leaking vacuum, but was told that it really wasn't a problem for this year of car. I may also add, that I have noticed when I get the car in a pull going up a hill, the air coming out of the dash vents switches to the defroster vents.

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Leaking intake gaskets are fairly common on nearly all engines from all manufacturers. Looking at long term fuel trims for each bank can help to tell what is going on. Even if the CEL isnt on, checking for pending codes might be a good idea.
 

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I have not had the anyone do any codes. I also have noticed that sometime while you are cruising at about 45 mph the engine will also raise and lower the rpm's. This happens when the car is hot, but is intermentent, not steady. Could a different sensor causr this problem. I am going to have the car checked tomorrow to see if any codes show up.
 

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If it's going up at the EXACT same interval as your A/C compressor running, that is the cause. It's a problem most people don't notice, but Ford made the lock/unlock of the torque converter too "sensitive" and the compressor cycling causes the torque converter to momentarily lock and unlock with the compressor. There is nothing you can do about it, and it won't hurt the car. That being said, if it's doing it at idle that isn't normal. It does sound like an intermittent vacuum leak. I suggest getting something flammable like WD40 and spraying around on the engine until the RPMs jump and you've found your leak. It helps to have an assistant for the WD40 procedure.
 

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The air comming out the defroster vents when going uphill means you do have a large vac leak. I would first inspect the pcv valve and hose for cracks/leaks. From there, check all the vac lines for cracks/leaks, wd40 works for that, so does starting fluid. Also, check along the upper intake gasket for leaks. Check with wd40 or starting fluid only when the engine is cold, as these are conbustable fluids, wipe off with a clean rag.
 

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I have not had the anyone do any codes. I also have noticed that sometime while you are cruising at about 45 mph the engine will also raise and lower the rpm's. This happens when the car is hot, but is intermentent, not steady. Could a different sensor causr this problem. I am going to have the car checked tomorrow to see if any codes show up.
45 under light throttle is usually the "lockup" speed for the torque converter. So that's normal.
 

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If it's going up at the EXACT same interval as your A/C compressor running, that is the cause. It's a problem most people don't notice, but Ford made the lock/unlock of the torque converter too "sensitive" and the compressor cycling causes the torque converter to momentarily lock and unlock with the compressor. There is nothing you can do about it, and it won't hurt the car. That being said, if it's doing it at idle that isn't normal. It does sound like an intermittent vacuum leak. I suggest getting something flammable like WD40 and spraying around on the engine until the RPMs jump and you've found your leak. It helps to have an assistant for the WD40 procedure.
:eek:???
 

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I have a 98 Taurus Se 3.0 OHV engine. Code "U" When I start the car up when its cold, the idle surges high/low. It does get better when it warms up. It surges so bad that when you hold on the brakes, it literally make the car jump/hop. I have replaced the IAC Valve and this made no difference. I have tried to find a vacumm leak, but cannot. Not saying there isn't one, just I haven't found any. Could someone please give me some great advice for this. I have read about intake gaskets leaking vacuum, but was told that it really wasn't a problem for this year of car. I may also add, that I have noticed when I get the car in a pull going up a hill, the air coming out of the dash vents switches to the defroster vents.

Please Help
Well, you definitely have a vacuum leak somewhere. It helps to have a handheld vacuum pump with gauge. Harbor freight has a cheap one
for $30 or so.

first, check the small hard line going through the firewall for the HVAC.
either the hard line can crack, or the small hoses can crack. If you have the vacuum pump, disconnect from the engine the HVAC line and pump
the dash side line down. If the vacuum does not hold, you have a leak under the dash and will have to trouble shoot there. If it holds, inspect all the little vacuum lines on the engine for cracking, chaffing or any irregularity's. If anything looks suspicious, replace it There are small lines going to multiple places including the fuel pressure regulator. look closely at them all.
 

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Same problem, looking for ideas.

Over the last several weeks I have had the same type of problem with my 98 SHO. So far I have replaced the IAC and TPS and also had the transmission flushed.

No improvement on idle surging and stalling which happens only at starting and stopping, at speed the car seems to run great with no apparent issues. I do not have any codes either, which I had verified by a Ford dealer.

Now I am up to the vacuum issue as well, and or considering replacing the ECU.

The only thing perhaps different with my situation, is that it happened shortly after I jump started my Mustang, hence I thought maybe I did some damage to the electrical system/ECU on the SHO

Could I have damaged the ECU? by incorrectly jump starting another car?

Ron
 
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