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Discussion Starter · #1 · (Edited)
So, I've been reading your forum for a while now and I know you get this one a lot, but I'm having that hesitation in my engine when I approach 4k-4.5k rpm. This is especially annoying when I'm trying to pass on the freeway and my car just says, "hell no." When I hit 4k, I get that bucking like the car is starving for fuel or hitting the rev limiter. Other then that, the car accelerates and shifts perfectly up untill that point on the powerband. My gas mileage is fine to. No abnormal smells, smoke or noises. Here's the list of things I've tried thus far.
1. Had the transmission checked, no problems.
2. Fuel Pump checked, no problems.
3. Just checked the fuel pressure, 45 psi like it should be.
4. Replaced the PCV valve
5. Replaced the thermostat.
6. Replaced the plug wires. They were registering 3-4 ohms, instead of the 6-9 like they should be.
7. Replaced the plugs last year, they still look good. Maybe I should re-gap them.
8. Cleaned the fuel injectors, they didn't look that bad though. I checked the ohms on those and it was 12-13 ohms. They should be 16-18, so I may replace those.
9. Checked the coil pack, resistance was 12.5 ohms, should be 13. Is that close enough?
10. I had the ECM reflashed by the dealership.
11. I don't see any issues with the exhaust. I have yet to find any glowing spots and my car did pass inspection and emissions last March. Plus I have no popping or sputter.
12. Replaced the air filter.
13. Checked throttle body and manifold, they appeared fairly clean, no sticking.

Things have improved a little bit. Before all this work, the car WOULD NOT get past 4.5k rpm. It would just sit there and buck, no speed increase. Now, my acceleration has improved a little, and I can get past 4.5k and on to 5k which some trouble. The car still hesitates a lot but it makes it through.
I don't know what to do anymore. I'll head to pick-n-pull to get a coil pack, fuel injectors and idle control valve if I can find some good ones. There's a 2005 Taurus, maybe I'll get lucky.
If these things don't work, what else can I do? This problem has been going on since November 2010.

Oh and the car has the Vulcan engine. It's a 2003 with 54k miles. I just replaced the oil, oil filter and coolant in the past two months.


Alright so today, I tested the vacuum and I found no issues. I tested the IAC valve by whacking it, no change in idle. I then pulled the plug on it while running, and I was told that if it was working properly, the car would stall shortly after, which it did in a few seconds. I tested the MAF sensor by unplugging it and driving, if this is broke, then unplugging it will stop the problem and it shows it needs to be replaced. Still the car was hesitating. I cleaned the MAF anyways, and still no change.

For now, I poured in a bottle of lucas oil fuel system cleaner, and I'm going to regap the plugs tomorrow. Just gotta see what happens with that.
 

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Discussion Starter · #3 ·
Clean the MAF and check for vacuum leaks.

Alright, I'll take a look at the MAF today.

As far as the vacuum leaks go. I haven't hooked any guages up to it but I looked over all the lines and didn't notice any damage or loose parts. Also I'm not having any signs of vacuum leaks; no rough idle, no acceleration problems at low rpms/take-off, and the scanner didn't return any bad results or codes.
If I do hook up a guage, where should I hook it up to?
 

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Discussion Starter · #5 ·
A normal 'engine at operating temperature' idle is 550-600 rpm. If yours is idling at 800-850, you have a high idle. Look closely at all the vacuum lines...one may have a crack in it.

Look around online and in haynes or w/e it's called. 800-850 rpm is acceptable for this engine. My idle it not high, it's always been at 800 way before this problem started.
 

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Discussion Starter · #9 ·
Just going by experience. Every Ford I have owned over the past 40 years (and there has been a lot of them) has had a warm idle of 550-600 rpm. That ranges from a 390-4V to the DOHC Zetec engine.

Sorry, I didn't mean to offend, I should've worded that better. It's just that I'm not having any other signs of a vacuum leak and I've read that my rpms are okay. I will still check for leaks more throughly though. I'll running out of ideas here, so I'll try anything.
I noticed the guage at the autozone has a connection to fit into the PCV valve hole...is that an acceptable location to test the vacuum? If so, what kind of readings would be normal for my car?
 

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Discussion Starter · #10 ·
It may be acceptable, but I don't think it's normal. An idle of 800 rpm tells me that the engine is compensating for something...either a vacuum leak, or a failed sensor, for example. This could be a problem that, over time, has gotten worse, and now you are seeing things happen as the problem gets worse. The higher idle could've been the first of those symptoms, even though it's been idling that high for a long time.

A failing IAC could be causing your problem(s). Have you tried whacking it??

I'll whack it today. All I want to do is whack that car right now...or have someone whack me and total it lol. My brother just got that lucky and now got himself into a nice 2011 Jeep Wrangler.

What should I look for when I whack it?
 

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Discussion Starter · #11 ·
Well, if the IAC is sticking, a GENTLE whack with a screwdriver handle should bring the idle down, and might, on the off chance, solve your problem. Sometimes a whack doesn't help, and you might have to take it off and try cleaning it. Also try what was suggested earlier and get some MAF cleaner and clean the MAF. Make sure you get cleaner specifically for the MAF, or you could damage it.
There are just so many things that can cause problems on these modern engines that it's very frustrating. That's why I am an advocate of learning what causes these problems, and learning how to diagnose..although one almost needs degrees in computer science, electrical engineering, physics and quantum mechanics.
Alright, will do. Thanks. As far as vacuum goes; what levels would be correct in my car? Also the idle rpm...is it possible someone messed with the idle adjustment screw?
 
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