Loping idle with a '98 Subauru 2.5

You could have a clogged fuel filter, if you haven't changed it in awhile. You could have a leak in the intake system somwhere also. When you slow down, you get less power to the engine. It may need spark plugs and wires as well, if in need for a tune up.

ENGINE LOPING CAUSED BY.LEAKING BY VACUUM LEAKS AT THE INTAKE MANIFOLD.CHECK ALL BOLTS ON THE INTAKE MANIFOLD TO MAKE SURE THEY TIGHT.YOU COULD HAVE LEAKING EGR VALVE OR PLUGGED PVC VALVE.DO A COMPRESSION TEST TO CHECK FOR LEAKING HEAD GASKET.DO A FUEL PUMP TEST CHECK FUEL PRESSURE.IT SHOULD BE 35 - 45 PSI.IF FUEL FILTER HAS NOT BEEN REPLACED.REPLACE IT FIRST IF FUEL PRESSURE TO LOW.DIRTY FUEL INJECTORS WILL CAUSE LOPING.TIMING CHAIN WORN.IGNITION TIMING OFF AND WORN LEAKING VALVES.AND WORN CAMSHAFT LOBES.ALL ABOVE WILL CAUSE ENGINE LOPING OR SHAKING.

So did you do all this to fix the loping or the loping came after the repairs? you have a 4cyl or v6??? Find someone with a scanner to check the PIDS.(scanner data)

This car has a very possible chance of having either a slightly bent valve, causing the loping idle, or the belt was installed a tooth off on the timing, it's one of the two.easiest way to deduce this would be to recheck the timing belt marks, to certify they're correct, then to do a simple compression check, get back to me with any questions, I'M HERE TO HELP!!!

Any time that the check engine light comes on, it indicates that the computer has found a condition serious enough to require service action. Rent a scanner, read the code(s), and pursue to repair(s). The scanner will clear the trouble light when the repairs are complete.

Check the exhaust manifold gasket. I have a 2003 SVT Focus I had a problem with it loping at low RPMs. I had a free flow exhaust system. When I bought a new exhaust manifold I replaced the gasket and the problem went away.

try timing i set mine at 4 degrees btc,dont forget to unhook your distributor bypass located behind your distributor

heavier oil if you are not in a cold climate. but before you do that have the oil pressure checked. We used to use a can of STP every once in a while on a motor in a dodge we had... nothing wrong with it... was just noisy.

Robert

its a vacumm guys check all your hoses with a carb cleaner while engine on be carefull not to let it catch on fire with the spray ok give it a slight of puff of it with the spray ok!! remember truck hoses are old and cracking ..

***** is correct adn yoru issues are not a quick fix.. some sensor is acting up and /or computer is being told to do something .....get full scope done and dig towards cause that way