Toyota 2.7 4cyl running rough- questions...

Tacoma747

Tacoma747

Well-Known Member
Joined
Mar 20, 2005
Location
Winston-Salem
Started running rough back in the beginning of June at Tellico, I had it out that same week for a test run at uwharrie and it ran fine, the only thing I changed in that time was I put hydro assist on. It had been in the basement since mid Feb. while I was swapping axles.

I have since replaced spark plugs, fuel filter (filter seemed to help SLIGHTLY), and have ran some Seafoam through the intake as well as added some in the oil, and gas. Ran it today at DPG, and the Seafoam in the gas never really seemed to make a difference.

It idles fine, and pretty much runs fine, I have not done much "investigating" on it to try to find the problem either. I stopped by Advance on the way home from DPG and got them to check the codes on it (95.5-OBD II), the only thing that came up was "Catalyst Efficency". It has a hi-flow cat on it, that has been there for quite a while, but is by no means "old". I am thinking O2 sensors are probably bad, but that same code has flashed before, but never caused the truck to run rough, so I never replaced the O2 sensors.

The only time it really seems to run rough, it can be at idle, and I hit the gas quickly, it kind of 'misses' for a second then revs up. If I rev it up SLOWLY, it seems to do fine, but still doesn't run great.

Any ideas? This is really starting to get on my nerves...
 
A quick demand for engine speed off idle requires a high vacuum, instant metered increases in fuel flow and appropriate changes in timing assuming all other factors (mechanical) are OK. Put a vacuum gage on it and see if its close to 20" steady. Put a timing light on it and see if the timing changes with engine speed changes. Sticking EGR, wet throttle position sensor contacts, mud on air filter, valves needing adjustment, plugs, wires, wet distributor cap, on and on.

Best of luck....
 
Some more info:

Vacuum 20" until I hit the throttle
fuel pressure out of tank 30psi, about 35psi when I hit the throttle
compression in cyl1:185+ cyl4:185+ (only two I checked)

It idles PERFECTLY. If I raise the throttle slowly, it runs fine, only when I nail it does it sputter.

I also cleaned the mass airflow sensor w/ contact cleaner.

Will mess w/ it some more tomorrow...
 
They are fairly new (past 20K miles probably). I put a new intake on it awhile back, I think I am going to take it off and put the stock one back on to see if that fixes it.

I would *think* if it was the plug wires it would affect it at all RPM ranges (maybe not so noticeable at idle).
 
Hooked a timing light to it today.

It seems the large pulley closest to the engine turns at a different rate than the other two... The middle pulley had a mark that stayed the same and advanced slightly (maybe 5*) when throttled up, but the large pulley closest to the engine was never the same... The large pulley seems to be loose or something? not REALLY loose, just slightly, is it designed to "slip"?

Don't think that would cause it to run like it is either. I also checked the tension on the timing chain. Could turn the crank aout 1/4" before the rotor button turned, so that should be OK.

Couldn't find any vacuum leaks...

More suggestions?
 
Now the funny part...

The AFM (mass airflow sensor) was the problem.. I had cleaned it off awhile back, but basically had just sprayed cleaner from inside the airbox over the sensor. Then Cperry said to clean it, so I figured I would take the top of the airbox off, sprayed it good from both sides, LOOKED clean...

Well, a friend's dad looked up the problem on a computer at work (he's a mechanic), and the airflow sensor being dirty was the main culprit.

SOOO, I took it COMPLETELY off this time (should have done that the first time :rolleyes:) cleaned it with contact cleaner, rag, and a pick, it was still VERY dirty.

Re-installed it, truck runs like a champ... All that other work for nothing...
 
just mark it down as experence.
glad you got her up and runnin.
btw nice work on the 4 runner cage.
look forward to seein ya sometime.


dawg
 
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