Outer Limits 4x4 Board

My sierra has developed a highrev/surging problem. I've got a toyota 4-age engine in it, and I'm running the original 92 sierra airbox with a K&N filter in it. It will idle normally when I first start it, but as soon as I drive a short distance it will either idle at 1200rpm, or it will surge between 1200 and 900 rpm when stationary. I did a search, but only found links to daihatsu forums where it was suggested to spray in carby/injector cleaner or to check for air leaks. The injector cleaner hasn't helped and I can't locate any leaks. Have any of you with 4-age conversions(or other efi engines) had the same trouble, or know if this is a common problem with an easy fix?? Any help would be appreciated!

replace your temp sender. that one thing that i know will cause it to surge like that but there could be other things

oops Tonka

could be alot of things, but if its chasing at idle could be the hego (O2 sensor) isnt switching correctly, check to see if it pluged in. what sort of air flow meter do they have? or MAP sensor. it might be a compresion prob maybe check your valve timing and engine timing. its not a miss that your feeling? hell it could also an idle up input to your ECU have you got A/C fitted that may not be in wworking order, P/sterring? and yeah like flyinwall stated your CTS could think its cold(wouldnt explain the chasing tho). start at the beging you said its a k&n filter but they do get blocked. If thats ok check your idle speed controller, not sure what type they have but may need to be cleaned while your there clean your throtle body. That done check your base idle (may be hard to do if its chasing real bad), check to make sure the PCV (positive crank ventilation) is ok, should rattle when shaken. make sure your vacume hose to the fuel reg isnt leaking and when was your fuel filter changed or is it even the right one for that engine. following that nah put a vacume gauge somewhere in the manifold see what its doing and go from there

which type of 4age do you have & what computer are you using.
first check the accel linkage & dashpot
check the coolant lines going to & from the throttle body + air valve,then check the tps
try that for starters let us know how you go

Thanks heaps for all you suggestions, I will get in this weekend and give it all a good going over. My main concern is that it has been running fine for over 6 months, and has only just started playing up for a month or so.

To answer some of your queeries.... from what I can tell, it is a 3rd gen 4AGE(89-91 with a T-50 toyota 5-speed gbox) and is MAP sensored. I'm running the computer that came with the engine so I'm assuming its stock. The accel linkages and throttle body are good and clean. Fuel lines/filters are good(nearly all new), the K&N filter is 3 weeks old as I thought maybe the engine might not be getting enough air through the old paper filter. I don't have air con, or power steering. I feel the O2 sensor is a bit iffy, as it is mounted in the 4inch rubber intake hose with silastic holding it in place, (came mounted this way) and has no apparent leaks.

I will check coolent lines, replace the temp sender and work through all your other suggestions over they weekend, I'll let you know how I go..

Thanks again Chris

Whitey wrote: I feel the O2 sensor is a bit iffy, as it is mounted in the 4inch rubber intake hose with silastic holding it in place, (came mounted this way) and has no apparent leaks.

I will check coolent lines, replace the temp sender and work through all your other suggestions over they weekend, I'll let you know how I go..

Thanks again Chris

you must be thinking of an air flow sensor or air temp sensor ( something along those lines not to sure tho, as i have never had the oppertunity to work on one). But the hego and O2 sensor are the same thing and mounted in your exhaust manifold some where (if extractors are fitted it sits just after all the pipes come to one).

The hego (O2) sensor is an input to the ECU (computer) telling it if the engine is running rich or lean and then the ECU adapts accordingly injecting more fuel if lean or not injecting so much if its rich. Depending on what type of idle speed control unit the ECU has over the engine (if any) it will change that also. if its sticking can cause an eratic idle, over fueling at idle and low speeds or even cause the engine to stall at idle. The hego only sends feed back to the ECU at idle and low speeds as the efficancy of your engine becomes alot better the faster and hotter its going (to a point).

Another thing to consider is the exhaust gas recirculation (EGR) could be stuck open allowing exhast gas back to the air flow mixture when it shouldnt.
schools out kids, hope it all makes sense and is right sure someone will let me know if its not

I had a 4age motor in my corolla SX. It had the same surging issues.
My mechanic said it was a vacumm hose. Forgotten which one as it was a few years ago. Just letting you know that it seems to be a common fault with the 4age motor.