1989 MasterAce Delayed Response Gas Pedal, Rough Idle, "Limp Mode" Woes

Hey ToyotaVanTech group! Long time reviewer first time poster.

For almost a year now I have battled with a friends 1989 Toyota MasterAce Surf Grand Saloon (4WD and Right hand Drive).

When he left it with me it was running fine, perfectly good idle. Since then I have had gas pedal delayed response, rough idle, battery thermal runaway, and now just no start at all.

Timeline:

September 2024

Throttle "limp response" first starts. It is oddly noticeable after or during left hand turns (not sure if relevant) and would basically feel like when pressing down on the gas, the engine was bogging getting too much fuel and fighting to stay running. When stepping off the gas the engine RPMs would sometimes increase. If this was a carbureted vehicle I would 100% say it was running too rich.

After this occurred a few times and the van returning to normal, it started causing the van to lose almost all engine power and shudder almost to a halt. It would sometimes recover if I worked the gas pedal up and down but mainly would die stranding me.

October 2024

I checked a few things, replaced/deleted the fusible links around the battery thinking they could be an issue, and took it for a test drive. During this test drive of about 40miles, the gas pedal issue occurred still, and in addition the van had a full battery melt down. The friend who left it with me stated he may have left the battery terminals under-torqued, or looking at the thread it may be that the alternator sense line was stuck at full output on the FL0.5. Still not sure why the battery melted down.

December 2024

After this and two tows home I left the van sitting while I tried to find a shop in Santa Cruz that would be willing to work on it. During this time I reviewed some threads on people stating similar loss of power from the ECU capacitors. I removed the ECU and checked all the capacitors for leaking. Seeing nothing I returned it back to its location. Not wanting to get stranded again without finding the culprit I left the van sitting.

Now

I have recently found a shop that is willing to take the van in, but wants it to be movable. I was able to get it started and idle slowly forward and backwards, but after awhile the idling van would shudder to a halt. If I put it into drive it would shudder and try to die as well especially if the gas pedal was pressed. After idling to a halt this afternoon now the van refuses to start at all.

My feeling over this issue has always been around electrical and fuel. During all of this there has been no check engine light, the only light that will occasionally come on is the orange oil level light (although oil level is fine). Because it is the Japanese right hand drive variant many of the great blog posts about it don't resemble the actual layout which further aids my frustration (check connectors that don't exist, mirrored components, unable to get trouble codes) and none of the manuals in English are aligned with what I am actually seeing in the van.

Things I have checked:

• ECU
• Fusible Links
• Fuses
• Battery
• Alternator

Things that were replaced prior to it being left with me:

• Clean tank
• fuel pump
• fuel filter
• fuel sending unit
• spark plugs
• water pump
• clutch fan
• all belts
• idler pulleys
• both radiator hoses
• throttle body hoses
• all heater core hoses
• transmission cooler
• transmission flush

Things I think it could be:

• ECU
• EFI System
• Fuel Pump
• Air Flow Meter
• TPS

My main question is if anyone has encountered these types of issues? I am pretty stumped.

Thanks in advance.

B

Well, yeah, not with a toyota van, but with a nissan prairie/stanza. 2 times actually. First time it was the air filter, I think it was the factory fitted 25/30 year old air filter, it was completely impermeable, it ran perfectly without it. So obviously I replaced it. To my surprise the issues started again after a year… it couldn’t possibly be… but no, the muffler had disintegrated, and the fibers that were in it completely blocked the exhaust.

but yeah, i think i would start with the basics, see if it has air in, air out, check if it has strong spark (remove 1 plug, hold it against a ground), check the spark plugs, if they are wet or dry. (Oversimplified: Dry=no fuel, wet=bad spark) If you have the tools, check fuel pressure and compression (although i have never done the last, i just dont want to know :rol:)

Thanks for the reply Jan! I have checked out the air filter and just replaced although the prior didn't seem to be fully clogged. I also have checked out the exhaust while the van is running and its definitely exhausting from the engine and not blocked, albet it does smell rich. Since this post the van has started up after sitting for 24 hours, which is very odd. I still am circling around fuel/electrical systems due to the sporadic intermittent nature of this issue. I think the next step would really be to check the compression as well.

Thanks again for getting back

I'd do a fuel pressure check. My '84 van had similar symptoms. I could start it in the driveway and it would idle, but when I tried to drive it down the street it would stall and then be hard to start. The more throttle I gave it, the faster it would stall. Sometimes I had to push it back down the street into the driveway. I did a fuel pressure check and the pressure was less than half of the spec in the service manual. I changed the fuel pump and then the van drove fine.

Hey Guys,

Update I was able to pull a code 8 from the diagnostic connector after finally determining where to short.

From the manual I have I believe on the JDM variant this points to the air temperature sensor thats integral to the air flow meter on the intake.

I am not fully sure how this sensor could cause the hesitation issues I am seeing, but atleast I have something pointing somewhere.

Thanks

Blaine

Did the air flow meter fix the problem?