YFZsandrider

My '94 22re pickup started having a problem with surging idle. When i start it up cold in the morning, it seems to idle pretty high, at about 2200 RPM, then will reach 2500 within a few minutes. After about 3 or 4 minutes of warm up, the motor will begin to surge in idle speed, bouncing between 1300 and 2000 rpm. It will do this for several minutes, but eventually seems to clear up.

I'm only on the second day of this problem, so I can't say with certaintly that it is an issue isolated to initail warm up, but its is really bothersome.

I don't know if it could be related to temperature, but it has been unusually cold here for the past couple days (around 30 degrees). Also, what should the normal cold start warm up RPM be for winter time?

camo31_10.50

somewhere above 2000rpms..i think around 2200-2400...at least thats what it is for my 22R carb'd motor..

as to why it's doing the surging.. i dont have a clue LOL

xxxtreme22r

sounds like the throttle position sensor, or cold start injector

abecedarian

I would expect cold idle to be around 1500-2000 max, higher or lower depending on ambient temps.
I'd rule out the cold start injector immediately since it should only operate during cranking; once the engine starts, the ECU controls the fuel mixture directly through the fuel injectors and compensates for temperature based on the coolant temp and intake air temp sensors. However, the auxillary air valve also operates to allow air to bypass the throttle and raise the idle speed when cold, slowly closing as the coolant and engine warm up, hopefully dropping the idle down to the stock 750 range.

Checking the TPS won't hurt anything. In particular you want to verify the TPS contacts IDL and E2 show less than 2300 ohms with the throtte closed so that the ECU is in open loop mode (ignoring the O2 sensor) during warm up. http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

YFZsandrider

I'll check the throttle position sensor. It makes sense to me that the TPS would be screwing up the idle speed consistency, but could it also accont for the idle speed being fairly high(above 2,000 RPM) during warm up?

Also, if I can't get to this for a couple days, is it going to hurt anything, other than my ego, to drive it with the surging idle issues?

Thanks for the help!

akyota1990

did you check to make sure you dont have any vac leaks some leaks cause a low idle some cause a high idle and some make it surge, i dont think it will hurt any thing but your mpg or emissions

whokrz

As abecedarian stated it is normally the air by pass which on yours should be on the underside of your throttle body. When mine failed it was open which causes an unexpected vacum leak once the engine was warm just like your symptoms.

YFZsandrider

So, I've been watching this problem a little closer... and I've determined that it consistently will begin the surge a couple minutes into the startup, and continue until the engine is fully warmed up. Once warm, the problem goes away.

turboboost

Hehe, I remember starting my truck one day when it was -45 out and I forgot to plug it in. The thing idled at 2800 RPM. lol.

Green_slime

i had the same problem on my izuzu amigo i had and it was the throttle position sensor went bad change that it should fix the problem

YFZsandrider

If my TPS is bad, wouldn't it throw a check engine light?

Also, whats a good place to buy a Denso (OEM) sensor? None of the auto parts shops around here have them.

xxxtreme22r

bosch o2 sensors are just as good.

tps sensor will not always throw a code from my experience. Had one go in my BMW and no CEL. And that thing monitors EVERYTHING!!!!

whokrz

Does it surge when you take your foot off of the brake?

Kinda a shot in the dark, but it might be a temp sensor
Basically the air bypass would be open because it is not controlled by the ecu. This would cause a high idle. If the temp sensor was shot the ecu could thing that the engine was at operating temperature and cut the fuel when the brake was applied.

xxxtreme22r

delete me wrong thread haha

whokrz

Now I feel better, I am not the only one that does this.

xxxtreme22r

I just posted up a strange idles issue thread. thought it was that one. Was wondering why the guy mentioned about the ecu taking over the fuel cut and the IAC not working because of a temp sensor. haha I have none of that.

YFZsandrider

You might kinda be on to something...

My radiator has been slowly loosing coolant through a small leak at the bottom. I had been topping it off every couple of days, but have been real busy for the past week, so I went to top it off this morning and it has propably a few quarts low. After filling it, I didn't seem to experience any problems for the rest of the day.

As far as the idle surging when I let off the brake... During the warm up period, when the engine seems to run high, and will eventually slip into a surging idle, there is a VERY noticeable drop off when the brake is slightly depressed. It feels like the fuel is being cut off when the brake is touched.

Does it seem like this low coolant level could be screwing with a temp sensor?

thedanned

A few quarts? Like almost a gallon low? I think you found your problem.


The low coolant issue causes a fluctuating idle because the air bypass valve is controlled by engine coolant. Unlike modern vehicles, the air bypass valve is a mechanical valve (a bi-metallic spring) that is heated up by the coolant and closes when warm. So low coolant
= your air valve is not closing = ECU freaking out because it knows the vehicle is warm but the idle is still too high so it tries to correct the high idle by cutting fuel.

But to answer your question, yes if you had an air pocket circulating in there the temp sensor would get alternating warm and cold readings, further freaking the ECU out.

whokrz

As thedanned stated it sounds like air where coolant should be.

YFZsandrider

Started it up this morning with a perfect idle. Problem solved... almost.

The collant was about 3 or 4 quarts low, so yes around a gallon. But before seeing this problem in the past couple days, I would still have an idle speed that is somewhat inconsistent. I can set the idle speed at 750, but it will still sometimes sit at around 1,000 RPM at lights.

I think I'll start out with running a function check on the TPS, then go from there.