This is not an idle problem. The car idles and runs fine, making decent power and gas mileage. I've done an extensive tune up, and keep up with all maintenance. I checked the small vacuum lines. I tested the TPS and the voltage change is very smooth all the way to 4.5 volts. I disconnected and plugged the evap vacuum lines and it still did it. I blocked off the FITV the correct way, and I had this problem before and after. I changed the fuel filter, and tested the O2.

The problem happens all the time after the car warms up, if I'm cruising between 2100 and 2600RPM, light throttle with a slight incline, the RPMs buck up and down between 2100 and 2600 RPMs. It will do it constantly as long as I keep the throttle at the same position and stay in the same gear. It doesn't do it at any other RPM.

Often if I let off the throttle suddenly, the engine bucks once instead of decelerating smoothly. This isn't a downshift. If I come to a rapid stop, often times the RPMs dip very low before climbing back up to idle speed.

Occassionally I notice a shuddering from the engine when cruising at 1600 to 2100 RPM, light throttle, on a slight incline.

Could it be some kind of weird vacuum brake booster problem that doesn't show any symptom to the braking system? Just a guess...

It's a D16Z6 swap with an appropriate ECU, using the DX fuel rail which doesn't have a fuel pulsation dampener, the DX exhaust manifold. If you need any other details please ask.

If anyone can successfully diagnose this for me, I'll paypal you $10 bucks. No random guessing though, there has to be some reasoning behind it.


Modified by shaundrake at 11:43 PM 5/5/2005

 

Am I invisible? Is it impossible to diagnose? $10 bucks people. TEN BUCKS.

 

How long have you had the problem? Since the swap?

 

I'm a D series retard, does that motor have an EGR on it? Clogged EGR valves and ports lead to hesitating and surging at light throttle like you're talking about.

 

sounds like a problem one of my friends had. his car would buck when creaping in a gear visiously... it was on his b16a2 in a 00ex... never figured it out.. good luck!

editr are you talking about more of a hesitation??

 

Thanks for the feedback.

Had the problem before and after the swap. So it's something common to the car and not the engine. The only things besides the obvious that are the same before and after the swap are the exhaust manifold back, O2 sensor, fuel line, fuel rail, and wire harness. That's all I can think of right now.

There's no EGR.

This is the problem as best as I can describe it. I'm cruising along anywhere between 2100 - 2500 RPM, and only in that range, I start to climb a slight incline but still cruising, the tachometer starts to surge from 2100 to 2500. You can feel the whole engine speeding up and down. Vroomm, vroomm, vroomm. Indefinately. Each surge lasting about 2 or 3 seconds. If I give it more throttle, downshift, or allow the RPM outside of that range, the problem goes away.

Seriously, if anyone can cure this I'll buy them a nice dinner $10 via paypal. If you're in San Diego and you think can help me but only by seeing the car in person, hit me up.

 

Is the engine all stock?

Fuel filter clogged? Ignition Timing set?

 

Engine is stock except for a POS AEM intake. I did the coolant bypass eliminating the FITV for a block off plate and gasket. But I had the problem before and afterward, and I had the problem with the old engine which didn't have the coolant bypassed.

Ignition timing is about 17 degrees advanced. The Harbor Freight adjustable timing gun sucks though. I set the gun to 0, and set the timing using the normal method. Then I check the timing at the TDC mark and the adjustment on the gun reads 18. Still within spec, but if the gun was accurate, the TDC mark should line up when the adjustment **** is at 16.

I just changed the fuel filter. The ECU hasn't set any trouble codes. Maybe I have a split personality that taps the throttle when I'm cruising.

Keep them coming.

 

Fuel filter? Weak fuel pump?

 

I changed the fuel filter.

I changed to a GSR fuel pump and I changed the sock on the pump. I checked the voltage to the pump.

Thanks for your input.

 

Have you considered testing or even replacing the IAC? People often make the mistake of thinking that the IAC is responsible for only the idle of the car, this is incorrect. The manufacturers are to blame though for naming it IAC (Idle Air Control/ler) instead of IRCC(Intantaneous Rate of Change Control), which is what it actually does. The IAC's most important function is creating a smooth deacceleration...which you mentioned you were having trouble with - "Often if I let off the throttle suddenly, the engine bucks once instead of decelerating smoothly. This isn't a downshift. If I come to a rapid stop, often times the RPMs dip very low before climbing back up to idle speed.

Occassionally I notice a shuddering from the engine when cruising at 1600 to 2100 RPM, light throttle, on a slight incline."

Don't take my word at face value though! If you want to actually research this you can download Holley's 950 Commander manual, in which you will find "Minimum IAC Position – This table allows the user to cause the IAC to “follow” the throttle position. As the throttle is opened,
you want the IAC to open also. This is to keep the engine from stalling when the throttle is instantly released. The IAC will not
close lower than the throttle follower position, so you will want to set the throttle follower at zero for the idle TPS position and
quickly ramp the IAC open after that." The theory is the same, good luck.

 

Good use of a first post. I'll try messing with/replacing the IACV, since I assumed it was only open at idle like you said. This motor and the previous motors had different IACVs, but it's worth a shot.

 

Email me your paypal address or home address. I'll go to the junkyard probably tuesday or wednesday.

 

that is a nice use of a 1st post, interesting information man...


but i hvae one more shot if that doesnt work..

its more obvious but you said you were sharing o2 sensors from the old motor, why dont you try buying a new one???... its worth a shot... keep us updated

 

Tested the O2 and it's not lazy. It has the right reference voltage and the heater works. It's only about 6 months old now. Both engines are the same OBD generation so I don't see any reason to change it. Thanks for the input though.

I can't wait to get some free time to go scavenging at the junkyard.

 

Okay I changed the IACV, no effect on my problem. So if someone can diagnose this for me it's $15 Paypal or MO.

The problem is that when I'm cruising between 2100-2500 RPM, holding the accelerator steady, the RPMs surge up and down about 300 RPM.

 

do you have a fuel pressure regulator? i had this problem for the past week, it was actually a combinations of problems, #1, where i had my tach wire running to my distributor, the electricity was arching to another wire causing crazy hesitation. i got that fixed, and also my fuel pressure has alot to do with drivability. ive played with tons of pressure settings along with cam gear settings and ignition settings, finally last night i set my cam gear back to zero and put my fuel to 36psi w vac on. left the ign timing advanced and the car ran like a dream. too much fuel and i got hesitation, too little fuel and it ran slow and hesitated also.
if you dont have a fuel pressure gauge/fpr take a look into that and see if its maybe running way too lean/rich.

 

Yeah, I've been meaning to check the fuel pressure. Thanks for reminding me. It's a stock FPR. I do believe I have the same FPR on this engine as the last engine, so there's a chance that this could be the cause. The ECU hasn't reported an AFR problem, and I don't have any hesitation. But the FPR is vacuum driven and if it's faulty, it could concievably cause my weird problem. Thanks for the suggestion. I'll see if I can get to it today.

Does the D16Z6/ZC fuel rail come with a pulsation damper? I'm using the DX fuel rail and it doesn't have one.

An FPR or adjustable cam gear wont give you any power unless your engine is heavily modded. You need at least a cam and some head work, or a turbo to get any benefit. And then you will need to have it tuned on a dyno. It's good to experiment. I respect you for turning it back to stock. A lot of people just crank up the fuel, turn the cam gear to some HT recommended setting, and swear their car is faster despite the obvious fact that it's slower than before. Then they stubbornly refuse to "downgrade" despite the best advice.

 

pull the dizzy cap...probly full of orange coloer dust...sound liek the dizzy is goin gto me

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by suspendedHatch &raquo;</TD></TR><TR><TD CLASS="quote">

The problem is that when I'm cruising between 2100-2500 RPM, holding the accelerator steady, the RPMs surge up and down about 300 RPM.</TD></TR></TABLE>

So the car is actually accelerating and decelerating up a hill with constant throttle?

 

my h22 does this at very light throttle from 1000 up to 1500 rpm and my aic is not connected. it still does it, even after my tune but a little less now. its gotta be the aicv

 

Tried a different IACV already. No effect.

The dizzy is clean. It doesn't wobble. Rotor and cap are all pretty new and not dirty. I changed the ignitor. I changed the O ring.

I just got my CA smog inspection notice. This might lead me to the answer, or it might lead to a world of pain. They test it at different RPM. I hope they don't test at 2100.

dustin, I wouldn't say that a few hundred RPM is enough to decelerate, but the power definately changes with the RPM surging and falling. Overall it feels like the engine has less power in that range. I usually downshift when it happens.

 

Looks like its the lock up solenoids. The resistance is out of spec, and it doesn't seem to be doing it with them unplugged.

 

Is the O2 sensor OEM? If you unplug the O2, how does the car run?

I can't see the fuel pulsation dampner making a difference at low rpm - high rpm perhaps.

Could there be some odd interaction with the Z6 head and Dx manifold?

You replaced the ignitor, what about the coil?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by suspendedHatch &raquo;</TD></TR><TR><TD CLASS="quote">Looks like its the lock up solenoids. The resistance is out of spec, and it doesn't seem to be doing it with them unplugged.</TD></TR></TABLE>

you have an auto tranny?