Need Help with Surging

[bolokid]

My son and I recently purchased a 91 Festiva with 173,000 miles. The car has EFI with an automatic transmission. I have noticed that the engine surges at all speeds whether accelerating or cruising, in all gears and it does not make any difference whether the car is hot or cold. It has the feel of timing that is advancing and retarding. Has anyone else had the same problem? Thanks for any suggestions.

[FestYboy]

start looking for leaks in the intake tract. make sure the MAP an TPS sensors are hooked up and reading properly (this will require use of a digital multimeter). where is the distributer clocked to? how new is the fuel filter? are ALL your fluids up to snuff?

[Huli]

Re: Need Help with Surging

Spark plugs and wires too.

Mine surged a bit because my plugs needed to be changed.

[bolokid]

All bodily fluids are up to where they should be. I noticed that the thermostat is not operating properly. I am not sure how to check out the MAP but have a Ford shop manual and will check out the MAP and TPS. I do not see any cracked hoses for vacuum leaks. Will also check timing. I will let you know how things turn out.

[htc]

I had a similar issue a while back, check your distributor. Mine looked like a snowy winters day!

[Huli]

Re: Need Help with Surging

All bodily fluids are up to where they should be. I noticed that the thermostat is not operating properly. I am not sure how to check out the MAP but have a Ford shop manual and will check out the MAP and TPS. I do not see any cracked hoses for vacuum leaks. Will also check timing. I will let you know how things turn out.

Would you mind posting how to check the MAP? My Haynes has seen better days.

[FestYboy]

the MAP is a 5vDC ref signal system... PCM provides 5v to the MAP, the MAP has esentially a variable resistor in it that reacts to changes in pressure and the PCM then looks at the differance from the initial 5v ref signal. similar to most TPS systems as well (except ours, which is a 3 position switch)

[Movin]

All bodily fluids are up to where they should be. I noticed that the thermostat is not operating properly. I am not sure how to check out the MAP but have a Ford shop manual and will check out the MAP and TPS. I do not see any cracked hoses for vacuum leaks. Will also check timing. I will let you know how things turn out.

It takes a long weekend away from home in a cabin on the beach to get my bodily fluids where they should be

[bhearts]

mine did this today, but it was cause my alternator sense wired was coming undone a bit.

[Bert]

Happened to me awhile back (surging) and simply re-adjusting the dashpot fixed it for me.

[Movin]

Sounds like you are on the rich or lean side of the air flow sensor. It is not linear but stair steps up and down. The test is if you do not feel the surging at constant speed, only while accelerating.

[bolokid]

I pulled the distributor cap and the rotor and cap were corroded. The cap and rotor have been replaced and the car runs much smoother but the surging is still with us. The surging does not occur under acceleration it is most noticeable when at constant speed. I replaced the thermostat and air cleaner also. The plugs ooks good but I am going to replace them tomorrow. I have not checked out the MAF yet.

[XFSE71]

I ran a wire from the o2 sensor to a DVOM on the dash. Then while driving look @ o2 V. if ~.8V = rich if ~.2V=lean. if o2v is varying ~.8v to ~.2v then it's happy. From there the fix.