TACH FLUXUATES

[woodrow]

Well my car has 110ks on it and it's starting to act up on me. When i start the car, occasionly it will rev up and down at idle. i usally just give it some gas and rev it up, and this sometimes works but it also sometimes stays at high revs and won't go down. i have to shut the engine off and restart it. any ideas what the problem is, tps?

 

[SHOZ123]

I would suspect the IAC valve. It's duty is to maintain the proper airflow at idle to keep the engine running smoothly and is how the PCM regulates the idle speed.

Time to try cleaning it with carb cleaner. There will be soot on the inside of it. Ford recommends the replacement of the metal gasket when you do this. Not many people do.

 

[Hochness]

This may not be of much help to you but I'll tell ya anyways. My 98 did something similar to that but when I was on the highway. The RPM's shot way high and then way low and the car jolted like I was tapping the accelerator really fast repeatedly. Turned out to be too much airflow from my cone filter, so I had to remove it and put the stock airbox back on.

Good Luck!!!

Sam

Sam's 98 SHO Page

 

[SHOZ123]

"Turned out to be too much airflow from my cone filter, so I had to remove it and put the stock airbox back on. "

That's bogus, it was more than likely your TPS that was acting up. My cone filter has never given me any problems.

 

[jedhead]

I replaced the IAC valve on my '98 to fix a simular problem.

Bob

 

[SHOZ123]

I replaced the IAC valve on my '98 to fix a simular problem.

Opps, IAC is what I meant to say not TPS. IAC if it's an idle problem, TPS if it higher rpms.

 

[Hochness]

That's bogus, it was more than likely your TPS that was acting up. My cone filter has never given me any problems.

About a week after I put on my cone filter it started doing this and gave a SES light. The codes were "Bank 1 & 2 System Too Rich" which is too much air. Then it started to run rough and the RPM's went high and low and the car "sputtered". I removed the cone filter and put my airbox back on and the problem went away INSTANTLY. I couldn't tell you what an IAC is so I can't argue that that could have fixed my problem, all I know is that I removed the cone and put the airbox back on and the problem went away.

Sam

98 SHO Black

 

[mholhut]

Sam, did you try resetting the PCM by disconnecting the battery? I've found that '98's sometimes have a problem with the cone filter installation. Seems like the computer programming for the OEM setup doesn't know what to do with the added airflow.

 

[Hochness]

Sam, did you try resetting the PCM by disconnecting the battery? I've found that '98's sometimes have a problem with the cone filter installation. Seems like the computer programming for the OEM setup doesn't know what to do with the added airflow.

Yes sir I did. It worked perfectly fine for a while (1 week or so) until I got my Flows put on and it seemed to me that the muffler shop dinked with it and then it started doing this. I unhooked the batt. cable and the SES light went away but came back later that day and the tach started flucuating (sp?) and running rough so I took the cone out and it went back to running perfectly. Oh-Well, I'll try it again in a few months and see what happens.

Sam
98 SHO