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MIT MIT is offline
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Join Date: Jan 1999
Location: GA
Posts: 43
rough idle 1.8L engine

I have '74 914 1.8L with original FI system.
The engine have rough idle and I thought it's because of the air leak from vacuume hoses. So I changed all hoses last week, however it still have that symptom. Especially after engine get hot (i.e. after get off from the freeway),idle goes down to about 100rpm. The idle speed adjustment is already all the way to the right. Is this symptom relate with an airflow meter?
Please give me some advices?

Thank you.
Old 01-04-1999, 11:24 AM
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I've heard the gasket and o-rings on the oil filler cap can cause problems, try those next.

As for finding problems with FI systems allways check the ignition first. Change the plugs, check the resistence of the wires, check the coil, etc. As for a guess, look at the cylinder head temp sensor. It is one of the few things that changes with temp and can drastically affect how the engine runs.

Look at the Porsche 914 fans web site in the tech section there is a L-Jet vac hose diagram. If you replaced the hoses one by one you should not have switched anything, but maybe they were mixed up to begin with.
Old 01-04-1999, 01:33 PM
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Eli Eli is offline
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Have you checked your Preasure Sensor. More often this item creates the most problems. If the unit does not hold vacum get a new one. there are several places on the 914 club pages that show you how to check this unit.

Bad idle aften goes hand in hand with vacum leaks. Just when you think you have replaced everything and fixed all the leaks, surprise. the best way to check for leaks is to use propane. Get a small tank like the ones you use for a camping stove. You will need to get one with a valve on the end, Atach a peice of ruber hose to the valve, turn on the gas, place the end of the hose near any suspected leak sources. If there is a leak your RPM will drop. Do this in a well ventilated area and use commom sense. this system works better than spraying startinmg fluid or break cleaner and less mess.

Old 01-07-1999, 07:22 PM
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The stock 1.8 did not have a manifold pressure sensor. Instead, it has an air flow meter.

OK, first step in any FI diagnostic procedure: always, always, ALWAYS check your ignition system. Make sure you're getting a nice fat healthy spark. Check the timing and dwell, examine your points to see if they are burned, pitted, or worn. I had bad points cause very similar problems.

Vaccuum leaks are a popular source of L-jet (the 1.8's FI) problems. Try checking and/or replacing the fuel injector seals; they're cheap and relatively easy, and they can leak when they get old and hard. Try to check for leaks between the intake runner pipes and the heads. Also check the "manifold boots", which are the short fat hoses between the plenum and the intake runners.

Check the resistance of the head temp sender, which is located near the #3 spark plug. Check somewhat lower and a little forward of there on the sheet metal. The resistance between its connector and ground should be 1500-2500 ohms when cold, and much less (~100?) when warm. Haynes has some values, but I don't remember if they have anything about the "hot" values.

Speaking of Haynes, they actually have a reasonable amount of data on checks you can make to your L-jet FI system. Things like head temp resistance, checking the decel valve, checking the air flow meter, etc. It is worthwhile to read those sections and start testing.

If you order one from Pelican, you help to support this site. Besides, you won't find them that much cheaper anywhere else!

Old 01-08-1999, 02:56 PM
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