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engine tune up

Hello all,

I own a 2001 Jeep TJ Sport with manual transmission. I've had this car for almost five years and it has been very reliable. No problems at all and drives very well. Other than regular oil/filter changes, air filter changes, tire rotations and replacing the spark plugs I have not done any other service to it over the years.

I've noticed that over the last year the gas mileage seems to have gone down, especially in city driving. I've also noticed that since about a month or so it has been idling rough for the first 30 seconds after starting the engine. Then it stabilizes and the engine idles just fine.

Recently I've also had intermittent problems starting it. A mechanic checked the spark plugs, throttle body and a few other things but couldn't find a problem other than the battery being run down. I replaced the battery and since then it has been starting fine again. I should mention that I used to drive it to work every day, but for the last six month I only drive it on the weekends. That could explain the older battery finally being worn down.

My question: Is there a recommended engine tune up that I should do to get it humming again and maybe improve on the gas mileage? Should I do something like a fuel system flush? I realize that going five years without a tune up is probably pretty terrible. What does a tune up really entail, what should I expect the mechanic to do?

Any kind of advice would be appreciated.

Thank you,

- Frank

Reply to
FW
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That's idle on warm-up. The O2 sensor is not a part of that stage so it's likely a crudded up throttle body and idle air passage. (link later)

Start with the easy stuff.

Clean the throttle body Idle Air Passage, helps to keep a smooth idle. That is probably the cause of your rough idle.

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You don't have to take the throttle body off. What ever you do, do not run the engine with the stepper motor removed. It basically destroys the part.

If you do take the TB off, remember the TB bolts only get torqued to about

9 ft.lbs and check the gasket to make sure it isn't cracked. If it's cracked, replace it. The bolts holding on the stepper motor go in hand tight, about 7 ft.lbs. I always keep a spare gasket. They are cheap.

Replace the upstream O2 sensor. (a weak sensor can cost you 1-2 mpg)

If I recall correctly, your fuel filter is in the tank, so replacing it isn't easy. I'd instead go grab a bottle of Chevron Techron fuel system cleaner and drop it in. STP also makes a fairly good one. Make sure they say O2 sensor safe. Routine use of decent fuel and the occasional tank of something like Texaco premium (more solvents) helps keep the injectors nice and clean.

If you really ..really.. want a squeaky clean engine, search out someone that uses the motorvac system.

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an engine kept in good shape won't need this. It's more forfolks that do not do routine maintenance (oil, plugs, etc), have a lot ofshort trips where the engine never heats up fully, or use crappy gas. Never underestimate the power of a nice long drive on the highway.

Another thing. Check over all the vacuum lines. Look for cracks or hardening by where they are joined to the intake.

Reply to
DougW

Hi Doug,

Thank you for the feedback. Sounds pretty easy and I'll definitely go and do it.

If anyone else has other suggestions please send them along.

Also I should mention the Jeep currently has 90,000kms on it.

Cheers,

- Frank

Reply to
Frank Worsley

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