Causes surging What should I do if my car surges occasionally?

not told RPM of surge. (full range of surge)
hot engine surge, or cold or both?
it's old most do this old.
lots of causes.
but why tells the reasons
the IAC is bad or just lost control of engine for 50 other caused.
let say engine as huge vacuum leak
the PCM closes the IAC and can not correct the massive vacuum leak.
or engine goes lean?
or spark misfires so bad IAC can not correcthis.
bad engine, bad spark bad fueling can and will make IAC go dead.
in fact fixing IAC is last, in my book
if all is good just cleaning IAC fixes it. some times.
or replace it.
on old cars the ECU surges the IAC if spec idle speed can not be reached, 800 hot.

Clean Throttle Body (both sides, not just what you can see) and MAF (mass air flow sensor) [spray and shake to dry].

https://www.google.com/search?q=2001+Ford+Focus.+running+rough+and+power+surges
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Hello. It seems your Cadillac is getting too much air into its engine; causing it to 'surge'. This could be due to a malfunctioning/defective vacuum brake booster. If your Cadillac's catalytic converter is 'clogging'; this will cause the engine to 'surge' too. Good luck and keep me informed; if you want to.

When was the last time you had the chain replaces or cleaned and lubricated it. A badly worn chain will cause a surge at medium speed and revs. The fact that it occurs when you hit a bump does suggest to me that it is the chain.

Questions here are better with full 'year make model' instead of generic '318'.

A few generic ideas.

1. Check fuel pump pressure.
2. Run injector cleaner through the fuel system 'Extreme Clean' is a good one.
3. Clean the throttle body.
4. Does it have a MAF (mass air flow sensor)?

More ideas here

https://www.google.com/search?q=1989+Dodge+318+stalls+and+surges+when+starting

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Replace fuel filter and check for fuel leaks. Check and change the pollution canister or purge valve.

Hi there:
IAC (Idle Air Control) valve is mounted on the throttle body held on by 2 screw. You might have a vacuum leak. You can find vacuum leaks with a can of WD40. Spray it all around with the engine running and if you hit a vacuum leak the engine will speed up for a second or two. Vacuum leaks are the most common problem causing this type of symptom.


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clean the MAF sensor with carb cleaner if you have one in the big air intake hose. Small heated wires inside. Causes lean mixture

Fuel pressure Normal range is 35 to 70 PSI. Without the proper fuel pressure needed the vehicle surges and looses power especially goin up hill and at WOT(wide open throttle) . Its a good call if you change full filter your going to any way. you got a surge going on. Also check the airfilter once that plugs up it will also cause the surge. Surges happen when it lacks something so your getting less of some thing

Dirt may have got onto the O2 sensor, this could cause a surge without the light coming on. Some debris may be on a sensor preventing the computer from making correct adjustments.....