Iceman4193

Problem: My idle speed will change depending on the outside air temperature. Cold days will have a high idle, hot days can have a very low idle. With high idle, I have the issue of a surging idle when applying the brakes, which from what I understand is the ECU cutting fuel flow to the injectors.

Additional Information: It is a 94 22re, not in great shape as I am in the process of building a replacement. At one point I accidently unplugged the MAF plug and broke the solder points on the board inside. I resoldered them and checked the Ohms for proper resistance and everything checked out. I don't know of any vacuum leaks but it is possible.

I think it would have something to do with the MAF unit because I believe that is where intake air temperature is read but before I buy another for like 200 bucks I wanted to see what you guys thought.

kbpickens

If you're building the replacement (stated), and it's the same engine (guessing), and you'd be buying a new MAF unit (guessing), why not buy a new one, put it in as a test, and see how things go?

Marsheen

Okay, before you start spending money on stuff verify a few things, I have a 3vze that had a similar problem, I know he 22re and 3vze cold start systems work the same. So first of all are you aware that coolant passes through a cold start valve near your throttle body? Start your check there first, I'm not exactly sure where the cold start air bypass valve is in on 22re but I know it's near the throttle body, just going by memory on my buddies engine. First thing you want to do is warm up your engine, and make sure hat hot coolant is traveling to that bypass valve via touching it and feeling whether its hot. Second your surge is actually caused by the cols start injector mounted on your plenum. The computer thinks its cold, when you press the break you cut the fuel supply directly in to the cylinders and the computer dumps fuel into the plenum to compensate. How to check and make sure its that? you warm up your engine, when it starts surging pop your hood and unplug the cold start injector. Drive again and see if its still surging. If your both not getting hot coolant to the air bypass valve, and test proves that it's the cold start injector causing the surge, you have a coolant problem. either a leak or a blockage, pressure test your cooling system and go form there. On my 3vze I had a return pipe cracked right in the V valley under my intake. and It was a 3.25 in long crack that was just dumping coolant, replaced it hadn't had a problem with high idle or surging ever since.

Marsheen

https://www.yotatech.com/forums/f116...-story-290615/ here is my thread where I explained some of the issues with my truck including the surge and high idle.

Marsheen

This was my problem

scope103

Surging idle with brakes applied is usually a leaking vacuum booster; it "uses" so much vacuum that it is injecting too much air into the plenum, which raises the rpms. The ECU does not cut fuel flow to the injectors at idle or during braking.

If you're concerned about the air temp sensor in the VAF, you can test that directly, just as you did the potentiometer and fuel control switch

The idle speed is SUPPOSED to be higher when the engine is cold. That is primarily governed by the ECT sensor (which is easy to check with a multimeter) and the Auxiliary air valve. https://acad-eng-gen.ca/ether3al.com...35auxiliar.pdf Not as easy to check, but here's the page of the manual.

Masheen may be conflating a bunch of things that happen when your truck starts. The cold start injector is a separate fuel injector that sprays extra fuel into the plenum. It only does this when you are cranking, and when it is cold. And if you have to crank for "too long," it shuts off before it floods the engine. The temp measurement and the timer is controlled by the Cold Start Injector Timer. Since the CSI only works when cranking, it almost certainly does not affect idle speed.

The throttle bodies have a coolant passage, but they are very different between the 3VZE and the 22re. I've referenced the manual page for the 22re.

Before you spend too much time on the harder tests, be sure the throttle linkage is working correctly. If the idle seems high, just pop the hood and press gently on part of the linkage to close the throttle plate. If the rpms drop and stay, then something is binding the throttle linkage, and you just need to find that. (By the way, don't oil the linkage; it's a dirt magnet and it will only work for a little while.)

Iceman4193

I can give the CSI a look, however the idle speed changes with outside air temperature, not engine temperature which is why I thought it would have been the IAT sensor. I do have a small coolant leak somewhere around the throttle body but since I am putting in all new coolant lines and components I was not too concerned with finding it because the system holds enough to keep in temp range.

Iceman4193

I had originally thought it was the booster as well, however when the idle is lower, particularly on hot days, I get no surge which should not be the case if it was a booster leak. It would surge all the time.
From what I have read in many other posts, the ECU cuts some fuel flow to the injectors when braking. If the idle is set to high, it causes a surging.

I had figured it was the VAF because it is more dependent on outside temperature than anything else (The changing idle speed). I tested the resistance on the circuit board when I re soldered it and it checked out but maybe it got messed up again. I'm not sure.

osv

is it throwing any codes?

i've never heard of a 22re engine cutting fuel flow when braking, in order to do that the brake light circuit would have to be wired into the ecu, so that the ecu would know when the brakes were applied... i can't think of any reason why it should work like that, the only thing that cutting fuel does is change the air/fuel ratio.

Iceman4193

Nope no codes, I forgot the thread that I saw that said that about the braking thing but I originally had my idle set to high. I turned it down after reading that and it fixed the problem. However, the temperature issue started happening a little while after that but what still holds the same if that the surging only happens when the idle is high. It will not surge when braking when it is hotter out and the idle is low.

MudHippy

Idle speed going up and down slightly depending on OAT is normal....to an extent. I usually have to adjust my idle speed for winter, spring, summer, and fall. Why is this you ask? Because cold air is thicker than hot air. And these engines don't have a means to self-adjust for that. Or for changes in altitude. Which is basically for the same reason. Air at lower altitude is thicker than air at higher altitude. Not to mention differences in oxygen content(which isn't really worth mentioning as far as its effect on idle speed, since your idle speed will still tend to raise with a climb in altitude, even when/if the oxygen content of that air is lowered).

osv

i seem to remember that the original megasquirts had this problem of picking the fuel curve based on one initial manifold air pressure sample, at engine startup, so when you made radical changes in elevation, the manifold air pressure would be significantly different than when you first started up the engine... you'd have to restart the engine to get the ecu to pick the correct fuel curve for the lower air pressure at altitude.

of course the oxygen sensor is always constantly trimming air-fuel ratio in real time, with both that megasquirt speed density system, and our afm-based efi systems, but it's a narrow-band sensor, with limited capabilities.

since our air flow meter efi system doesn't have a manifold air pressure sensor, how does it determine the air density(aka altitude)?

"The two final portions of the AFM are the intake air temperature sensor THA and the fuel pump contacts FC and E1. The THA circuit is just a temperature sensitive resistor in series with a fixed resistor (R) inside the ECU and the ECU "sees" the voltage across THA to ground and uses this to determine the temperature of the intake air, which affects its density. And since the density of the air affects how far the AFM sensing vane is pushed open for a given volume of air passing through it, the ECU needs to know both the temperature and the volume or air in order to estimate the mass (or weight) of air (or oxygen) coming into the engine."
http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml

i see a couple of possibilities:
1) sticky tb linkage, like scope said, if it's acting flaky pull over, pop the hood, and fiddle around with the linkage, see if it changes the idle behavior
2) swap out the afm box entirely, or at least look at the air temp sensor in it, since the symptoms appear to be temp-related.

i'm not sure that any of that addresses the surging issue, tho.

Iceman4193

Would testing the AFM for proper resistance on the circuit for the temp sensor be enough? I had originally done this when I had to resolder it but something may have happened to it.

osv

resistance testing is about all you've got, short of swapping the entire afm out.

my question would be, what is the "temperature sensitive resistor" that's inside of the afm, and how do you test that?