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HDGENE, ASE Certified Technician
Category: Mercury
Satisfied Customers: 5130
Experience:  25 years experience Ford Senior Master Technician/Diesel certified ASE Master Technician
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1997 Merc Mountaineer. Changed mass airflow sensor, TPS and

Customer Question

1997 Merc Mountaineer. Changed mass airflow sensor, TPS and all 4 O2 sensors. Then ran 2 tanks of gas with high octain and injector cleaner. Engine still sputters when idleing and driving. Does not stall or die. It will not do it when the engine is cold, but always does it when the engine reaches operating temp. Computer will not throw a code. Changed plugs and wires 8k miles ago. Problem started about 2k after that. Ideas?
Submitted: 1 year ago.
Category: Mercury
Expert:  HDGENE replied 1 year ago.

Hello what engine is in this truck 4.0 or 5.0? SOHC or OHV?

Customer: replied 1 year ago.
5.0. I do not know of the SOHC or OHV spec, but I understand that they only put one type of engine in the AWD... which I did not put in the question, sorry.
Expert:  HDGENE replied 1 year ago.

Ok no problem, just needed to know what engine was in the vehicle, so it runs ok,just idles rough. How many miles are on the engine? No vacuum leaks? Any major engine repairs done recently and now having this concern? If you hook up a vacuum gauge to the engine is the needle bouncing a lot?

Customer: replied 1 year ago.
It is not in time... like a vacuum or timing issue. it acts like it is repeatedly briefly loosing fuel, as it does not smoke. 170K miles, no major repairs and have not put a vacuum gauge on it yet. Is there a sensor that controls a choke butterfly valve? Could that sensor failing make these symptoms occur? It it were vacuum, would it happen all the time or only when it is operating temp since it never does it until it is fully up to operating temp.
Expert:  HDGENE replied 1 year ago.

The idle air control valv controls the cold and hot idle. If a sensor was out it should set a memory code, Key On engine off on demand code or key on engine running on demand code if you havent run these tests and just pulling memory codes. With it running ok cold then having issues hot I woud suspect an issue with a valve seating properly. A vacuum gauge will tell if you have a broken valve spring if the gauge flutters.An engine compression test when the engine is hot will tell you more about the base engne condition.

Customer: replied 1 year ago.
I will hook it up and test the vacuum while it is cold and hot then get back to you.
Expert:  HDGENE replied 1 year ago.

Very good.let me know

Customer: replied 1 year ago.
I now have a new tool! Warmed the truck up to op temp, shut it off and hooked up the vacuum meter to a line directly connected to the intake manifold. Started truck. The meter held steady at 20 Hg. I had the engine revved to maintain 2K RPM and gauge then maintained at 20.75 Hg. I turned truck off, removed gauge and replaced hose. I drove the truck until it started the issue (4 miles) then returned home and shut off. Hooked gauge back up and started. When issue would happen (intermittently) the gauge would drop to the bottom of the hash mark for 20 Hg. When the problem was not happening it would read at the top of the hash mark for 20 Hg. The swing of the needle from the top of the hash to the bottom of the hash conceited with the engine running rough. This is the only time the needle altered from being steady.
Customer: replied 1 year ago.
Before I drove the vehicle, on the first test, I watched the meter at idle for about 5 minutes and then for 1 minute at 2K RPM. It did not alter at all until the problem in question presented.
Expert:  HDGENE replied 1 year ago.

If the vacuum is going negative, it could be a clogged catalytic convertor, if you loosen the exhaust to have a leak and drive the vehicle and the concern is gone I woul suspect a plugged cat.

Customer: replied 1 year ago.
I will see if the sucker is welded or clamped on the to header pipe. If I can do that, I will try and let you know.
Expert:  HDGENE replied 1 year ago.

It should have two nuts or bolts holding it to either exhaust manifold to seperate

Customer: replied 1 year ago.
If that works, do you think Cataclean would work or would it take more than that?
Expert:  HDGENE replied 1 year ago.

Hard to say,im not familiar with or have used that product

Customer: replied 1 year ago.
The truck got louder... lol... It continues to act the same. I changed the fuel filter and put the cadaclean in... as it cleans the whole fuel system and the cad. I am going to try and check the coolant temp sensor to make sure it is functioning. Any other ideas?
Expert:  HDGENE replied 1 year ago.

No, thats all I have to suggest at this time

Expert:  HDGENE replied 1 year ago.

Only other thing would be to check the pcv valve to make sure it isnt sticking to draw a negative vacuum