idle surge

[smilz]

I have a 1991 honda civic, 1.6l 16 valve maual tran

problem is it surges at idle, a big surge like maybe 1300rpm to 600 rpm, not sure doesnt have a tach, the speed also changes from a long surge to short surges when the ac is turned on. It has died a couple times. it lacks power. (like goes slow up hills and whatnot) yesterday it didnt even want to go when i steped on the gas. only wentwhen barely press the gas or stop on it .. it has code 5, which i believe is a map sensor code... if vacume line, wich runs to the map sensor is removed off the tps idle smooths out. the moter was just rebuilt, has good compresion. I believe the idle air control is good, it has new plugs and wires. no smoke from the exaust. also surges if holding the clutch in at higher speeds....any questions or ideas? help me please...man this is embarasing sitting in this car at a red light =)

[kelrx8-civicbeater]

clean out the iacv
my iacv was full of crap, but my luck it didnt help.
but it can be your problem unplug the iacv when its surging.also try sticking your foot under the pedal and lifting it up.should make it stop surging

[smilz]

I tried cleaning out the iac no luck also picking up the pedel makes no diference either. Could this be a leaky intake manifold gasket? trouble codes are still 5 blinks (manifold absolute pressure code) ...

[EF You]

then you need to check the vacuum line going from the firewall to your intake manifold. its plugged into a small black sensor on the firewall, and the plug for it has three wires. its just a small square sensor, not the cylinder one. chances are the hose has a leak, because map sensors dont go bad all that often (of course by saying this you are going to be the exception)

as far as surging, thats the IACV trying to compensate for something else being wrong. its trying to maintain an idle, and something else on your car is preventing it. after getting the map sensor code to stop, if it still surges, its the FITV. thats a small cylinder on your manifold, and it has two coolant lines going to it, and no electrical plugs. you need to take the end cap off of it, and inside is a button with screw type fitting around it. just take a flatblade screwdriver and tighten it. it loosens over the years.

[smilz]

ok could not get the map sensor code to go away, i replaced the map sensor with a known good one and still the same. I checked the voltage at the map sensor at 5 volts and on the return at the ecu, varys depending on idle. Rpm raised up it would be lower, at idle a bit higher..topped out at about 2.5 volts. ....so sensor is good and wireing to the sensor from the ecu is good as well......As far as a vacume leak (intake manifold gasket) doesnt seem to be... with the vacume line disconected from the map sensor and pluged it holds about 15 lbs of vacume constently...also the idle kind of smooths out this way, although runs like crap....Also compresion is even through all cylinders .................................................. ...
With a good map sensor and wiring what would\could trigger a map sensor code? Is that based on the amount of vacume into the map sensor, and or based on voltage input output at the map sensor, or could it be a conflict between the map sensor readings and that of other faulty sensor?, if so what other sensor ? ...i will check the fitv and let you know on that.