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1998 mustang V6 3.8L Base stumbles in Idle and hesitates in accel.

11514 Views 6 Replies 3 Participants Last post by  jj79miro
Greetings, I am a new mustang owner and here is my situation. 1998 mustang v6 3.8L the engine stumbles in idle (RPM are not erratic, constant 800 rpm). When acceleration between 1000 and 2000 rpm the car hesitates. After 2000 the hesitation is gone. Sometimes it does it, sometimes it don’t. does it while cold the same as hot.

I cleaned the IAC, MAFS, PCV, check all vacuum hoses, did fuel injector cleaner in gas tank, change air filter (it was dirty). When i disconnect the TPS the car does nothing it keeps running. When I disconnect the IAC the car dies.

I have not check the EGR or the taken out the TPS. So far no check engine light on.

Please help. I need guidance in this before starting to buy the valves and sensors.

Thank You
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That will be my nest step - 1998 mustang v6 fuel filter

Thank You. I will follow those steps and let you know as soon as they are completed.
did not think about transmission problems

The transmission changes smooth. I though about it, paid attention to the gears and is not in a specific one. It does it when I accelerate the car in parking also. I will double verify.

An update for today,

1. I used Sea Foam treatment to clean the intake manifold and the vacuum lines (straight to the intake and the brake booster vacuum line).

This improved the car start and acceleration. I does not hesitate during acceleration now.

2. I used Sea Foam transmission fluid treatment (1/2 pint)

Transmission feels smoother now. It still make a sound when changing from P to R and from N to D. I think that the mount might be going bad. I will verify that.

3. I check the spark plug wires and the resistance was 4.7 kohms is all of them.

Not sure if this is good or bad. Have read that less than 6.0 is bad. <Can sombody confirm>

4. I narrow it down to:

A. Stumbles between 1000 and 2000 RPM at park and while running.
B. I verified the TSP output signal and while accelerating it decreased from 4.22 V to 2.8 V. When stumbling the reading went to 0 (for a fraction of time) and then back to what it was.

I think I should replace it. Any comments appreciated.

I know is to much info but I tend to write like that. Sorry my grammar, english is not my first langauge. :grinroll:

Thank you:wavey
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The End - Fix it

Just to end this issue:

1. Computer scanner threw P1151 code. Problem was vacuum leak throug the PCV and engine mount vacuum lines. (Fixed)
2. Hesitation was caused by bad spark plug wires. I did resistance test and it threw 5 Kohms average. I did the night test and saw huge arc from the wires to the engine block. Replaced the wires and problem solved.

Now the car is running like heaven. RPMs when up to 900 in idle and acceleration is good.

Next steps:

1. Change fuel filter and spark plugs (if the wires were bad there is a change the plugs will go soon).

2. Perform complete vacuum test to make sure no more vacuum leaks.

3. Verify transmission for preventive maintenance

4. And complete the tune up.

Thank You for these posts and the others that helped me find the issue and fix it.
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