Hi All,

My 89 Formula 350 TPI is surging when I'm at idle, sometimes almost killing, then overshooting a few times before settling down--then repeats. At higher rpms, it's fine with good accelleration--no noticeable misses.

No fun crossing the border into Canada each day and having the crossing gaurd think I'm getting ready to take off before he's done asking questions.

I replaced the IAC valve, but it didn't make a difference. I have not changed spark plugs for quite a while, so that's my next project. I would like some opinions as to what people think would be the the top most likely causes.

Thanks,
-Brent

 

Check TPS voltage

 

well i have a 91 t/a with 305 tpi in it. And i just currently went through this problem. I would like to know a little more info on you situation to see if can be of some help. How high is the rpms jumping? In Drive ( if auto ) or neutral ( manual ) 600 is the ideal idle speed. Is it jumping up from 600 and then back down or is it jumping up and then dropping back down past 600? Also i found have realized ( atleast on my car ) if you have your tps set at excatly .54 you have a better response time off a dead stop. Most people and even the chiltons book says between .45 to .60 is good but i would suggest putting it as close to .54 as possible. But if you just replaced your iac and your tps is set right sounds like your computer is jumping in and out of open and closed circuit. But it also could be a faulty o2 sensor. Does it or has it flashed any codes? ( check engine light came on at all ) One givin maybe a little more indept description and a little more info i possibly could be of some assistance

 

Hi,

The rpms jump from 650 to ~1200, then back down to ~100, then up again and finally settles back at 650 very quickly While in Drive. If in Park or neutral, the idle jumps around from 650 to ~1200. NO codes are being set that I know of and the Check engine light has never come on. I have not checked the TPS voltage--maybe its been knocked. I will check that first and also scan it for codes.

Thanks,
-Brent

 

When you replaced the IAC, did you clean up inside the trhottle body where the pintle sticks in? It gets REALLY gunked and cruddy in that hole. I used an old toothbrush soaked in carb cleaner to clean mine out. Then spray more TB cleaner in the IAC air passages.

 

Have you removed or replaced any other stuff relating to the intake?

Also, a surging idea is usually a sign of a vacuum leak.

 

The other thing is if the car has the original injectors (which I highly doubt).

The OEM "mul-tec" injectors could be the culprit.