Surging / Cycling

Post by **ARCHINSTL** » Sun Sep 11, 2005 10:43 pm

Well -
Is anyone else (how many may be more accurate...) getting a "surging / cycling" from 1800rpm to 2200 rpm to 1800 rpm? This is noticeable at a stop, when revved to that 2000 mark. On the road, this is manifested in a stumble / hesitation (?), still at that RPM range.
This is evident when the engine is completely warm, so I am presuming the TVSV has something to do with it (mine is new, though). This is a recent phenomenon, though.
Any other thoughts?
Thanks,
Tom M.

takza · Post by **takza** » Mon Sep 12, 2005 5:25 am

I had something like this when I cleaned the EGR...almost undriveable. Can test if it's the EGR by plugging the vac line to it....if it's this... then you'd need to find what was confusing the EGR....

Post by **ARCHINSTL** » Mon Sep 12, 2005 11:58 am

Takza -
Thanks for the reply. You are confirming what I thought.
I actually super-cleaned/shined the totally clogged EGR a while back and prepared some photos on some mods to your Procedure (Thank You!). And just like you, it ran better with the EGR disabled. I went to the MO Emissions station last week with the EGR disabled, and it flunked on NOx and HC. So, I took the EGR out and cleaned the inside again, this time with oven cleaner to really get out any carbon residue.
Now the cycling mentioned is back, so it would seem that the EGR is having that effect. However, since the valve is functioning properly, I think that the vacuum modulator is the culprit. I found reference to problems with this on a Toyota Factory site through Toyotanation.com.
The FSM, as usual, tells you how to test it, but not what the results are if it does not test right. * Mine blows lots of air through port Q (to the steel tube), but very little air through port P*. The amount of vac through all of the steel tubes is fine, and the check valve is working too, so I suspect something internal in the modulator.
Anyone ever replaced the modulator - or had a similar experience?
I'm going for a retest tomorrow or so, but will leave the apparently malfunctioning valve hooked up this time - maybe it will pass at least the NOx...
Tom M.
> > > EDIT < < <
I should have stated "...it blows lots of air through port Q to the bottom of the modulator cap, but very little air through port P to the bottom of the modulator cap."

takza · Post by **takza** » Tue Sep 13, 2005 3:41 am

It's been awhile...but your modulator tests sound like what mine did...doubtful that air was flowing thru one port.

Not sure if hitting the ports with some WD40 or similar would loosen the valves inside or not.

Post by **ARCHINSTL** » Sat Sep 17, 2005 9:02 pm

Well-
I stopped the surging/cycling problem.
When it hit 2200 rpm, it would drop to 1800 rpm, and then repeat the cycle. This continually occurred whether at idle or whilst driving.
I had already replaced every single rubber hose, whether vacuum or fuel (including the 3 at the tank, which was "challenging"). The only hoses I had not replaced were the two to the brake booster. I replaced those, and on checking the 20 year-old OEMs with a gauge, discovered a TINY leak in the one closest to the booster.
And Hallelujah, Hosanna, and Eureka - the surging disappeared !
I would strongly suggest all doing this. This did surprise me. It stopped the surging completely, and obviously there must be a minuscule braking effort increase. It may also help some of you with hesitation; it did not for me, but at least one more item has been laid to rest.
A note on fitting the hoses: These are thick-walled , but not quite the same OD as the OE, and the OE clamps will not quite clamp as tightly as before. I then used 4 of the band-type, and also retained the one at the firewall for location. The hose I used is Goodyear SAE30JR9 9.5mm for fuel injection.
Tom M.