Engine sputtering / stuttering at 2500 rpm?
 

I have a 1999 4Runner SR5 with 208,000 miles that just developed a random issue when I picked my car up from my mechanic for an unrelated issue.

The engine is sputtering / stuttering at 2500 rpms. There's no check engine codes. It happens even in neutral. Anyone have any ideas as to what this could be?

My mechanic is very busy and he said he doesn't want to guess or throw parts on it and told me maybe I should just pay a dealership $150 to diagnose it.

What did you have done at the mechanic? What is the previous maintenance history?

This is my thread about that issue.

My mechanic texted me saying he "Installed the new fan clutch, replaced some hose clamps that leaked under pressure, replaced the radiator cap because I did not like how it felt or what it was doing... I let the car run about an hour temp just under the middle - $120 total"

Previous maintenance history link here

As far as the maintenance history is concerned, the only thing that catches my eye that I think could be related to this issue, is the new catalytic converter. I had to get that due to a "cat not ready" status for state emissions test, no check engine codes.

Do you have a Federal (1 cat) or California (2 cats) emission vehicle? Are you able to get the rpm's above 2500 rpm's? If you can does it clear up, get worse, or stay the same?

Federal, stay the same or worst. Didn't really try to push it. I'm not near the vehicle right now or I'd test it further for more solid answers.

Well there went my clogged cat theory... Do you have a way to scan it? It might have a pending code if you're lucky. I see that you did spark plugs in 2019, do you remember if you did spark plug wires at the same time?

Battery terminals, fender ground good. Clean the maf and see how it does. If problem still there then look at fuel pump, filter, injectors.

If you can get your hands on the FSM, test the Throttle Position Sensor. They can go bad, not throw a code, and cause the engine to stumble or even stall.

Update: This is the Toyota Dealers diagnosis

Crankshaft sensor: graphing crank sensor shows senor is breaking up around 2500-3000 RPM. Replace crank shaft position sensor and removing timing covers to inspect for damage to crank timing gear/trigger wheel

Question: Anyone have the part number for this?

I tried searching the forums but not finding much

Replaced crankshaft position sensor with DENSO 196-1109.

Issue fixed.

Side note: Expensive for me ($300 labor only) because apparently someone broke the bolt head off and my mechanic struggled with it for days. Or he could've broke it and lied (which I doubt but?), who the hell will ever know.

Dealt with some new rapid stuttering, even at idle.

Problem & Solution: No check engine light, pending misfire code, ended up being some loose spark plugs.

cps
 

how do you access the crankshaft position sensor?

Final Update (hopefully?)
 

Update on this issue. Hopefully the last one.

Haven't driven much since the sensor issue. 2500 miles later, new issue. Currently at 211k with the issue fixed.

New stuttering: engine loosing power at idle and while driving after 30-40+ minute drives. Rough idle after engine driven 30-40+ minutes. Able to drive it but engine sputtering, max 45-50mph.

I replaced the spark plugs (6) and the wires (3) with NGK. Problem solved.

Old wires were NGK with only about 50k miles on them. The old spark plugs were the same NGK Iridium plugs, with only 40k miles on them, but dirty. Could possibly be due to valve cover gasket leaks, which were recently replaced.

I would recommend Denso plugs. A lot of reports of them lasting a really long time.

Did you check for vacuum leaks? I wonder if a vacuum hose came loose or broke on one the previous repairs.

Edit: For some reason my missed the part "problem solved" I need my coffee.

For plug I wouldn’t use anything that didn’t have to prongs. It says right on the engine not to use single prong plugs