HDMac07

In need of some help here, guys. Recently pulled the motor from a ‘92 Pickup (22re) that had a timing chain wear through the cover. Ended up putting a new head on from YOTA1 Performance as well as replacing tons of parts with new OEM stuff along the way. Plugs, wires, cap, rotor, IAC, aftermarket EGR from 22re performance, full OEM gasket kit, fuel filter, adjusted the TPS.. you name it, I did my best to cover it. The truck runs and drives excellently for the most part other than one issue.

When I start the truck in the morning it runs like a dream. Idles up perfectly until it’s warm and settles down right at 900rpm. If I don’t start the truck again until I leave work at the end of the day, it still runs perfectly. Where the issue lies is when I have to restart the truck after an hour or so of sitting. So, say I drive to work and the truck gets to full operating temperature and then I need to restart it 45 minutes later I end up getting a low, rough idle that seems to fix itself only after driving it for a bit. It is very consistent, I can duplicate the problem daily. Once I put a few miles on the truck, it’s like the problem never occurred. It sorts itself out each and every time. It’s definitely not a normal condition, when this is happening it’s only running half as well as it does when I start the truck after sitting for LONGER periods of time.

To make it even more frustrating, I have no codes. Timing is perfect and will changes with E1 TE1 jumped just as it should. Tested the TPS, cold start injector, cold start time switch, coolant temp sensor, vacuum switching valve, and so on all with readings within spec. Can not find any vacuum leaks and the vacuum gauge reads perfectly. I tested the AFM while in the vehicle and all resistance readings at the pins are within spec. What I have NOT done is open the MAF to test the mechanical function of the AFM and I have not tested fuel pressure while it is in the poor running state.

I’m stumped as to how it can run perfectly until everything is heat soaked and then and ONLY then does it start running rough. Like I said, if I drive it a few (5 or so) miles it sorts itself out. Problems like this tend to get worse over time, and the low/rough/miss feeling at idle when the problem is occurring is an uncomfortable feeling to say the least. I’d really like to get it solved and I am willing to listen to any suggestions!!

akwheeler

Still have any of the old parts? put the old IAC back in and try it, same with the EGR. I am grasping at straws and I don't have a solid idea what it could be.

Paul22RE

I have a similar problem and also changed out a ton of stuff to no avail, even tried another TB. However, mine happens as soon as I restart after truck reaches operating temp. Please let us know if you figure it out.

Co_94_PU

iTrader: (-1)

It's almost certainly a mixture issue, it's either running the warm up enrichment program or the fuel pressure us wrong..

Get a couple of those cheap digital volt readouts from eBay to monitor the FPU switch and the engine coolant temp sensor. You can also use these on VTA and THA (VAFM, TPS) to catch any flakey behavior.

Paul22RE

So the signal to the FPU VSV comes from the ECU after reaching a certain temperature? I wonder if that could be my issue, not getting 12V to that solenoid after car is hot? (I tested VSV and it works as it should, but maybe it isn't getting signal to activate?) Also noticed my idle ups fine when A/C is on at startup, but idle drops after operating temp is reached thus causing A/C clutch to disengage. The same signal from ECU controls both FPU & A/C VSVs?

However, 4Crawler bypassed his FPU VSV and has no issues with hot starting: http://www.4crawler.com/4x4/CheapTri...ne_Pix/10.html

Also, anyone know what the 3rd VSV (with a red plug) is for on the valve cover? (Blue is FPU, Gray is A/C)

Co_94_PU

iTrader: (-1)

Two temp switch's for FPU and Idle up, they have separate signals (wires). Iirc these two switch's work opposite of each other, one opens when hot the other closes when hot.

The FPU vsv exposes the regulator bias port to atmosphere, it's usually plumbed to vacuum which causes the diaphragm to open and reduces fuel pressure at idle. So it's intended purpose is to give a little less fuel when it's not needed, and a little more fuel during hot starts. There is a TSB that specs a different temperature range for the switch, to help fix hard/rough hot starts.

There are various revisions of the ECU hardware and software involved, combine this with local differences of air density and temperature.. What works for someone might not work for everyone.

Do you have an EGR system, there is a vsv for the vacuum modulator.

Paul22RE

Yes, I have an EGR system, so that explains the 3rd VSV.

How can we test that the FPU switch is working properly at hot starts? I assume by switch, you mean the solenoid in the VSV?

HDMac07

I could be wrong, but I’m not even seeing the FPU switch on the engine of my 1992. I’m familiar with where the switch is on the older 22RE’s.. near the thermostat. Am I missing something here?

Co_94_PU

iTrader: (-1)

No I do not mean the vsv, tsw is the signal name on the wiring diagrams. I'm not sure of the temperature range it functions in off hand. You can use your multimeter to see if it changes States from open to closed. Same with the FPU signal. You can check the state of the vsv with a clean section of vacuum line to see which port is open. You can also check the fuel pressure with the vacuum vs without.

RAD4Runner

Hi folks, Happy 2020!
Don't have much to share, except that despite all the logical fixes/ maintenance I've done to fix the intermittent hard-warm-rough-idle, it still comes back, especially this cold (San Diego... BRRR! - LOL!) season.
VEEERRRY intermittent. My hypothesis is there's a certain combination of intake air temp, coolant temp, engine compartment / fuel line temp where the ECU just does not address well.
I have not been quick enough to look at my fu3l pre55ure gag3 when this happens. Could be that ECU does not turn the VSV on in temp range above.

Co_94_PU

iTrader: (-1)

I accept that hypothesis is very feasible (RE: the temp switch TSB!)

Wide band oxygen sensor with a log function that triggers off the STA signal? Being able to log some of those other input and outputs would be helpful I am sure.. You could probably get away without the expense of a wideband sensor and just throw a "simple" MCU circuit at it. One that logs simple stuff like air temp signal, engine coolant, CSI timer and FPU state? Maybe a trigger button to do a hard save of the data outside of the cyclical log area, you know so you can worry about what got logged later because most of us can't just stop our day to dive into logs we got in the car to be somewhere in a somewhat timely fashion.

Seems well within the capabilities of an arduino or MCU of your preference.

In the end I expect the end results to be similar to Toyota's solution of changing the range the temp switch flips. That being the cheaper solution than recalling ECU's and throwing a bunch of cash/time into reprogramming.

toyoda addict

I have pretty much the same issue OP describes. It started when I replaced the IAC valve (new aisin). Fixed the original issue but started the low rough idle on warm starts. It is frustrating.

Co_94_PU

iTrader: (-1)

Going to have to be more specific unless you just want a consolation hug, or a higher post count...

What we are talking about here mostly is the random hot rough start due to air fuel ratio as commanded by the old 8bit 80's era ECU/CPU fuel table.

toyoda addict

I dont want anything. I was just stating that for me, installing a new IAC valve somehow caused the issue discribed in the op. I'll leave you guys to it.

wallytoo

iTrader: (1)

i know this was posted months ago, but not all 22re trucks had the FPU vsv. also, you might check your idle speed; 900 rpm seems a bit high, considering the spec for an '87 22re is in the 750-800 rpm range (22re - 750, 22rte - 800).

wallytoo

iTrader: (1)

have you pulled the vacuum hose on your FPR during the rough idle? (checking for presence of fuel in the line, meaning the FPR is leaking)

Co_94_PU

iTrader: (-1)

How certain are you about that statement of not all 22re had a vsv on the FPU vacuum line? (FPU is on every ECU pin map of 22re I've ever seen, to the best of my recollection.)

TSW might not be there, but the vsv should be wether the vsv "got lost by a PO" is a separate issue. (Who has a picture of a smooth thermostat housing that doesnt have bungs or tapped bungs even?) And yes some TCCS computer adjust the injectors without a FPU but the 22re I don't believe is one of them not even the first generation computers ("EFI ", pre TCCS, from the first run of 85's)

All these parts, TSW and FPU vsv, show up in 86, 87, 88 and 89-94 service diagrams. (Can't find my 85 manual, but I'll wager a $3 bottle of fat tire it's there also).

..
What I read he isn't seeing is a switch in the thermostat housing, based on " near the thermostat "

Again never seen a legitimate 22re (22r might be smooth or not tapped i don't recall off hand) thermostat housing without a port for TSW.


.. Typed out to much to want to go back and quote the second response ..

I think by that point the sparkplug is already wet and causing the misfire so changing the fuel pressure by pulling the vacuum off the regulator which causes more fuel per injection pulse is the wrong way to go. The plug needs to dry off and you've got two choices, let it sit and evaporate or Rev it till it clears.

wallytoo

iTrader: (1)

eh, as certain as i am of the underhood sticker on both of my '87 4r's.

edit: in the diagram, the green dashed lines are for 4wd equipped vehicles, and the diagram shows the fuel pressure up VSV as being used only on 4wd vehicles.

RASALIBRE

The FPU VSV function is only to expose the FPR to atmosphere. Other than that the FPR is controlled by manifold vacuum.

FPR under full vacuum=low fuel pressure=less fuel
FPR to atmosphere=high fuel pressure=more fuel

The 22re is batch fired injection so fuel is present before it’s needed, the excess fuel eventually evaporates off over time.

A person could surmise that at a hot dead start there is no reason for higher fuel pressure because of latent fuel still present in the runners and at the back of valves that hasn’t evaporated off. The ecu operates this vsv anyway resulting in higher fuel pressure, causing a rich rough hot start condition.

The FPU VSV can fail and leave the FPR exposed to atmospheric pressure at all points of operation. Running higher fuel pressure at all times is not always optimal.

Pretty simple to test. As others have mentioned, just run a vacuum line from the FPR straight to one of the ports on the manifold, bypassing the FPU VSV.

RASALIBRE

Here’s the only reference I could find as to what the FPU VSV does and when it does it.


Here’s a good link in general:

https://www.aa1car.com/library/fuel_...ion_toyota.htm

“RESIDUAL FUEL PRESSUREIf an engine is hard to start when hot, fuel may be boiling in the rail because the system isn't holding residual pressure when the ignition is shut off. To prevent vapor lock and reduce the cranking time when restarting the engine, a check valve inside the fuel pump holds the pressure in the line. Toyota says pressure should remain above 21 psi for five minutes after the engine is turned off. If the system fails to hold pressure, either the check valve or pressure regulator is leaking, or an injector is leaking. Regulator leaks can be ruled out by pinching off the return line. Injector leaks can be checked by removing the fuel injector and rail assembly from the manifold, and pressurizing the rail. No fuel drips? Then it's the pump check valve.”