Cutting out mid throttle, stumble at idle (1 Viewer)

[AKSean]

I did a search on the forum and found a few semi relevant threads but not exactly the same as the issue I am having.

It’s a 97 with 180,000, we have put about half those miles on and it’s been a great rig.

It will start right up, idle high for warm up and then when it kicks down it will stumble and sometimes catch and idle fine for 30 seconds and then stumble again and die eventually.

While driving at mid throttle it will sputter bad, but the engine rpms remain steady. Give it full throttle and it kicks in. At full throttle it has no problems.

There was some corrosion on the battery terminals, cleaned that up and it solved the problem for a couple of days and then went back to doing the same thing.

It seems like an electrical problem. Plugs, wires, cap, rotor are not that old. Cold weather could be a factor as it didn’t do it until it got cold. Intake air temp sensor?

TPS?

Just replaced the fuel filter, didn’t help.

Open for suggestions.

It’s been a while since I posted here and couldn’t remember my log in so new account.

 

[gummycarbs]

My original TPS was causing surging at heavy throttle on hills.

Replaced it with an NTK and the surge was fixed. A few months later I started having an intermittent stumble. Like it seemed like the engine died and then it would catch and return to normal idle. It started doing thing several times per minute at idle, but I don't recall if it had any issues under power.

I replaced the NTK TPS with a used Toyota TPS off eBay, and it's been great for the last year and a half.

So yeah, I would probably try the TPS if I were you.

 

[AKSean]

Update - As stated in the original post I changed the fuel filter and initially at idle it didn't seem to make a difference. But, after a short drive the stumble went away and I have now driven about 30 miles and all seems to be good. It's still cold so that doesn't seem to be a factor. Hopefully that was it.

 

[Emerald80]

I’m experiencing a similar issue currently on my truck (1996). I bought it with the engine removed for blown headgasket by previous owner. I rebuilt the engine in August and it was running fine after. Bottom end bored 1mm oversized Toyota pistons, new bearings, decked block and head flat, lapped valves new valve stem seals. Replaced all vacuum and coolant hoses. New wires plugs fuel filter, all the usual tune up stuff. All new gaskets. Intake, throttle body, idle control valve, egr all cleaned up when motor was out. Everything is oem toyota except ARP head studs. Installed the engine and it fired right up, ran beautifully. Didn’t drive the truck very much after that, less than 100 miles before I stripped the body down and did a paint job. That took me like 3 months. I finally finished getting the truck all back together last week and I’ve put around 500 miles on it in the last 3 days since we just got snow. 120 miles of it was this morning, had no issues. Then around noon I drove it 2 minutes around the neighborhood and the engine stalled out while I was doing 5mph. Had to restart it 5 or 6 times to get back to my house because it kept stalling while i was slowly moving. Once in the garage noticed it had a rough idle. (Before, was very smooth). I checked for vacuum leaks for about an hour. Checked egr function, manifold vacuum, wiring connections, throttle cables, all check good. Then went for some test drives and found at part/ middle throttle I had no acceleration above 1200-1500 rpm, but if I put the pedal all the way down there would be a slight delay and then finally the truck would accelerate. I’ve read a few threads so far that made me suspect the o2 sensors. My connectors may have got wet from all the snow driving. I tried cleaning / drying them out and applied dielectric grease to keep water out but it didn’t make a difference. I then unplugged my battery for about 20 minutes. After that it ran great at idle. And no more weird throttle acceleration. issue. This lasted for maybe 15 minutes of driving then it stalled again in the neighborhood after a quick drive up and down the freeway (4 miles). I don’t know when my o2 sensors were replaced last but the truck sat for 6 years in the previous owners back yard. I think I’ll replace them tomorrow if I can get to a parts store that has densos in stock. I’ll let you know how it goes.
-Matt

Btw i found another thread with a similar issue where they posted a video:
My issue is exactly like his in the video. Trying to re-find that thread.

 

[Emerald80]

Bogs down under medium throttle - Solved

Scroll to the end of the post for the TLDR version. This is a 1997 FJ80 with 191k and maintenance being up to date, with no known issues with the engine or transmission. This was really weird. I went on a pretty long and rough fire trail for about 5 miles, nothing that was too extreme. I’ve...

forum.ih8mud.com

This is the thread that makes me believe it could be an O2 sensor issue. Post #13 convinced me to try the ecu reset by unplugging the battery. And like the original poster in that thread, my truck ran fine for a little while. Im guessing that the bad o2 sensor(s) could be causing the ecu to trim the fuel/ spark incorrectly for non-WOT conditions.

 

[BILT4ME]

Check the connector on the two temperature sensors on the head. The engine changes fueling when it gets up to temp, so if you're seeing a change when it reaches temp, it may be related.

Also, did you make any changes or cleaning to your MAF unit in the intake tube? Check the wiring harness there.

I also recall reading about the IAC valve not actuating properly when you get no power above 1500 RPM.

You can also reset the ECU by pulling the EFI fuse in the fuse box.

 

[Emerald80]

Update: I installed 2 new denso O2 sensors today. I had the battery unplugged for about an hour or 2 when I went out to get the sensors from NAPA and during the replacement. After replacing, drove it for 30 minutes down the freeway and back. Idles great and no weird acceleration bogging at part throttle. After dinner the wife and I went driving around the neighborhoods looking at xmas lights for about an hour to see if it would stall/ die on me while doing around 10-15 miles an hour again, no issues. Seems to be running better than ever. The sensors I took off were toyota parts (possibly original?). I need to drive about 500 miles this week for commuting to work, ill post an update Sunday or sooner if the problem reoccurs.
-Matt

 

[Squash]

Try #2 sensor for ECM water temp. One sensor is for the gauge while the second performs engine management.

 

[Emerald80]

Already put around 500 miles on it since replacing the 02 sensors and the issue hasn't returned. Idle is perfect now as well. I believe new O2 sensors fixed my issue. Hope this helps the thread starter if his issue returns.

 

[AKSean]

My issue has returned. I'll try replacing the O2 sensors. Appreciate the feedback.

 

[inkpot]

So, neither of you had a Check Engine light pop on?

 

[Emerald80]

So, neither of you had a Check Engine light pop on?

No check engine light on mine.