Is the check engine light on ? High idle speed could be a vac leak or a problem with the throttle body. Its possible the same vac leak is causing the rich mixture if the map sensor is reading correctly. The computer would think you were accelerating.
- If you need clarification, ask it in the comment box above.
- Better answers use proper spelling and grammar.
- Provide details, support with references or personal experience.
Tell us some more! Your answer needs to include more details to help people.You can't post answers that contain an email address.Please enter a valid email address.The email address entered is already associated to an account.Login to postPlease use English characters only.
Tip: The max point reward for answering a question is 15.
skipped filters?
hiccup.s can be lots of things,
so tell when the hicup ,er misfire happens
hot or cold engine. ? or both.
at any speed. , only fast right foot?, or only wide open throttle?
only on hills. ?
so far , no miss at idle or slow speed.
my guess, car unseen.
car has an A/T trans, and all A/T jump from park to drive
selection is made on a cold engine, due to the very fast idle speed.
what was the park and cold idle speed. and out door temps.
the lower out door temps, make idle speed , cold engine, even higher
but when the engine reaches 180F or more and holds, the RPM
is about 800 RPM (the FSM tells the exact amount and does vary for the unstated engine option) so at 800 the tranny don;t lurch, did it on a hot engine. so if idle speeds are wrong say so and say it with engine temps. or its all meaningless.
next :
runs rough, the engine (even parked?) is called misfire.
misfire on a good engine (full compression)
is:
1: bad spark (or never had a tune up ever) every 60k miles.
2: bad fueling. too rich, too lean (low idle) bad injectors (stuck or clogged, or wrong fuel pump pressure or bad Fuel pressure regulator)
3: bad fuel.
there is a test for each possible failure. all very simple test.
it takes $80 in gauge tools to find engine problems.
fast idle speed screw, works off the fast idle cam which the choke adjustment sets, it works together by linkages. This is the raised idle speed setting you need to keep a cold engine running. First you set the idle speed by the idle speed screw with engine at normal operating temperature. Then you set the linkage up so the cam is on a raised step, throttle will be held on that raised step. then you can turn the idle speed screw to get idle at about 1500-1800 rpm. Now when you start engine cold, choke will set the fast idle cam on that raised step- when engine starts and runs it should be running at your fast idle setting. That's how it supposed to work, you just have to get everything adjusted right. I hate carburetors, they never stay adjusted right. Considering their complexity and small mechanical parts, no wonder.
I have a 1988 5.7 gmc that after start up idles fine runs strong under
full throttle but at highway speed and under no load speed it sputters
and at slow speed it is running rich i have done complete tune up
rebuilt the tbi One concern i have is someone removed stock air cleaner
system and the one they installed has no intake air sensor could this
be the problem ? IT CERTAINLY CAN BE THE PROBLEM. The air flow sensor if a VITAL part of your fuel delivery and emmision's system. Your mixture is controlled by a computer that uses the sensor data from that device. If you possibly can get the old one, put it back on. It is possible that I may not be totally right about this point but the operation of your engine is dependent on all the parts being there. and also i have no codes and no ck engine light on. There may not be code for a missing part. That system is not perfect. I hope this helps, Happy New Year, Mark
tune up-read your plugs and then check your timing. use timing light and double check with scan tool-most 91 305's were high outputs which
requires higher octane than regular (fuel grade revelatnt to compression ratio and altitude) you may want to check fuel pressure could be a clogged filter or bad pump.
Fuel distrbutor could be going bad, also weak spark could be an issue. Should do a real tune up before trying to diagnose. Also duty cycle adjustment, but dont mess with that until you do a tune up.
yes checked fuel pressure and replaced the fuel filter, checked the mapp sensor,tested throttle position sensor, has strong spark, 50psi fuel pressure, fresh tune up, runs real rich and rough idle but wont rev up like fuel injectors arent speeding up, also checked exhaust. thanks julius
Hi there. First make sure that your engine is idling fast enough. If the idle is too low (below 750rpm), it is likely to stall on idle. You should also check for vacuum leaks around the intake manifold and associated black rubber hoses. Some people use carb cleaner spray to spray around the hoses and seal areas to check for leaks, because the engine will speed up if a leak is found. I rough idle can also be caused by a bad spark plug wire or fouled spark plug or even a overly rich or lean idle fuel mixture. So remove the plugs and check that the plugs are burning clean (no black soot or glazing). The plugs should be near white clean. If you find a bad plug, then follow the wire back to the coil. Verify wire is good such as testing with an ohm meter and comparing the reading to the others. A big difference would indicate a problem.
×