Engine Surging, Question about possible fix

[south59]

Hello guys,
Througout this weekend ive been trying to diagnose a surge during about 1500 -2500 RPM's which is very noticeable. I've tried cleaning the MAF, IAC and have checked the TPS. I unplugged the MAF sensor wire and started the Ex up, and just like that the surging was gone(the engine would hold 2000 RPM constant) EDIT: seemed to surge at a higher RPM after removing MAF connector.

 

[MrShorty]

While it isn't perfect, the first thing I would do if I suspected a bad MAF is run the EEC-IV self-tests (aka "pull codes"). The EEC-IV computer won't see every possible fault in the components it monitors, but it will see many of them. Codes can be pulled with little more than a paper clip -- see tests at www.dalidesign.com/hbook/eectest.html (unless you have one of the few EEC-V '95's).

 

[Billy177]

clean the maf first also try retorquing the intake manifols bolts

 

[south59]

Would a bad IAC cause this surging/uneven acceleration to happen? Engine is throwing a 411 code, 411 (R) Idle speed system not controlling idle properly (generally idle too high) - ISC.I was also considering changing the thermostat since the gauge stays close to cold all the time, tricking the engine. Any other reccomendations? the MAF is brand new fyi.

other things im considering:
pcv- hasnt been changed at all to my knowledge
tps-never been replaced.

 

[MrShorty]

If a 411 is the only code you're getting, then I would suggest moving on. It seems that particular code by itself isn't very useful, other than identifying that the engine is running rough, which we already knew.
I would go ahead and check the TPS and make sure the ISC (and maybe the whole throttle body, while you're at it) is clean.
Check fuel pressure and check FPR for a ruptured diaphragm.
Since you said unplugging the MAF helped, you might check the output of the MAF and make sure it responds properly.

 

[south59]

Small Update

I have noticed that even on hotter days here in Houston, the engine temp gets only about 1/4 up after driving for at least 30 mins, never even close to mid range. Would a faulty thermostat be the cause of this surging if the engine thinks its too cold all the time? I also have noticed a gas smell coming from the truck. The FPR doesnt have gas in the connector. I havent gotten any CEL's so this is very puzzeling to me. any ideas?

 

[MrShorty]

I wouldn't expect a faulty thermostat by itself to cause the idle to surge, but I wouldn't completely rule it out. If you know it's bad, replace it.

Gas smell, you say? Any gas in the oil? Cannister purge solenoid opening? Any gas leaks anywhere? What does your fuel pressure look like? PCV valve stuck closed?

 

[karl_burns]

I recently replaced my thermostat (two weeks ago) and I cleaned the intake / TB / MAF last spring. Yesterday, I noticed a very similar surge. It only appeared in the 1500-2500 rpm range. I've been meaning to replace the IAC for a while now, but this "surge" started very recently. It was like every couple of seconds, the engine had a lot more power (but only for like a third of a second). Like the entire explorer was bucking.
Weird. Any update South59? I'm a Houstonian living in Boston, so it's no warm air that's causing my problem.
Karl

 

[south59]

Yeah I pretty much fixed the surging, although its still there to a very small degree. I replaced the thermostat and cleaned the TB, & PCV with throttle body cleaner. When i took the TPS out to clean the TB, i noticed alot of sediment/dirt on the red rubber gasket on the manifold area...so i used a very small amount of electrical cleaner on a qu-tip to get it out. so im guessing the TPS was somewhat of the problem although it didnt throw any TPS codes. My IAC checks out fine as wells as the MAF. Ill be replacing the plugs and wires soon, which i hope will remedy it completely.

How is your idle ??

 

[karl_burns]

My idle is OK. Loves to drop down to 400 or so though.... Been like that for a while. I rpelaced plugs about 4 months ago, so I'm guessing the IAC or maybe TPS. Since IAC is definitely getting replaced, I'll clean the whole intake at that time too. If it continues, the TPS. Then I'll just plain get mad.
Karl