Low RPM hesitation

[wrgibson]

As the title states, I'm having a problem with a low rpm, low throttle hesitation. The problem is at its worst when the car is cold. In 1st through 3rd gear, when I'm cruising low rpms (<2500) the car seems to hesitate when I roll slowly into the throttle. Once the car struggles through a few hundred rpms, the hesitation just seems to "let go". I say let go because when it does it rocks my head back a little.

The problem seems to go away when the car warms up, but will sometimes show itself after cruising low speeds for a while.

I do have a vaccuum problem (only getting 14-15), and a boost leak on the throttle body at the TPS. My question is, could this vaccuum and boost leak be the source of my problem? I'm also thinking that it could be my MAF crappin out on me.

Just for reference: Bone stock RB20, FMIC, 3" exh.Thanks in advance!

[onepuff]

This an issue with the ECU. I have the same problem. See my posts here.

zer...20det

[onepuff]

If you had any type of consult program like Nissan Data Scan or Conzult, etc. you would see that the computer is retarding the timing to 7* up until around 2800 RPM or so. Here is a scan from Nistune guide where the warmup timing table is shown. Matt the Nistune creator recently discovered this table and will soon implement it into the software so it can be edited. This is the only way I know of to correct this issue. I am guessing Nissan put this in to keep the driver from driving the car hard when cold.

[eh?]

I do have a vaccuum problem (only getting 14-15), and a boost leak on the throttle body at the TPS. My question is, could this vaccuum and boost leak be the source of my problem? Thanks in advance!

That's where you'd start first. Find all your leaks and then move on.

[wrgibson]

That's where you'd start first. Find all your leaks and then move on.

I know I have a leak at the TPS. I've read that replacing the o-rings in the throttle body results in binding. Am I better off just getting a replacement rather than attempting to fix mine? Also, would an rb25 throttle body fit my 20?

On another note.....I thought rb20's run at 7psi. My stock 20 is running 11psi.....don't know why. Anyone have any insight?

Sorry for the long posts and all the questions. I'm just trying to get my car prepped for the upcoming auto-x.

EDIT: I do have the e-bay version of consult....calumsult I think...anyway, I'll hook up my laptop and run the car around to check those timing #'s. I recently set base timing to 16*. For some reason I think I remember seeing 16* being recommeded. Please correct if I'm wrong.

[onepuff]

rb20= 10-11PSIRB25=7PSI

[wrgibson]

rb20= 10-11PSIRB25=7PSI

Perfecto!

Now all I need to fix is that boost leak at the TPS and I should be good for the auto-x. Last time I searched for fixes for the TPS leak all of them ended up causing the throttle close to be slowed down by the new o-rings. Has anybody had any luck fixing theirs?

[mattleegee]

any updates?

[wrgibson]

I haven't been able to drive the car because my free eghey manifold cracked......go figure. haha.

Before all that, I ran the car around with my laptop in there to monitor. I don't recall the timing dropping. However, I definitely feel the car pick up right at 3000 rpm, whether I'm seeing boost or not, which leads me to believe that the conditional warm-up timing table could be my problem. Another thing that leads me to believe this is the car will run just fine as soon as water temps reach 150*.

I do have a boost leak at the TPS and a vaccuum leak (vac gauge reads 14-15). I'm sure that fixing both of these issues would help to narrow down the problem, but I have no clue where that vac leak is coming from.

[mattleegee]

what is vac supposed to be at idle, mine is at about 10 i think

[wrgibson]

what is vac supposed to be at idle, mine is at about 10 i think

From what I understand, vac should be in the neighborhood of 20, but I'm not positive. Hopefully someone who knows for sure will chime in.

[dekansnowman]

I have an RB25DET S2 and I'm having almost exactly the same symptoms as your are but my vacuum is a perfect 20. I noticed the sudden loss of stumble resulting in a smooth acceleration and even a quick drop in RPMs as soon as I shift. I mean the car won't die but the RPMs just plummet as soon as I push the clutch in. Car cruises and I get wideband readings all over the place. Sometimes I'm stinky rich and sometimes I'm off the chart lean. It slowly creeps in different directions so i'm so lost as to why that's happening.

[Newtype]

i had the same problem with my 26 and problem with mine was exactly what you said you already know is wrong with your 25.. Boost leak and vacuum leak. My leaks were coming from a different' source though my greddy type r bov. For those of you who are familiar with it know theres two vacuum nipples on it. Well theres a rubber boot on the inside of the head that acts as a seal and it was cut cause it got pinched between the diaphram. So vacuum was going in one nipple and right out the other so i was losing vacuum and boost cause the bov was chattering open and close until about 6 pounds of boost came on to hold the thing closed. So my motor was hesitating just like yours up until heavy boost, which was anything past 2500 rpms.. Hense the verdict fix your leaks and you should be golden..

[Sil240]

I would def checkout that boost leak then look about the coolant temp sensor.

My car read 21 in/hg at idle.But my car idles high sometimes.I gotta get my tach hooked up.

Snowman- Maybe your release bearing is bad..Or even worse the thrust bearings?????

Thats very strange, because the engine/ecu doesn't know when you push the clutch.So thats gotta be a physical problem.

[Jermaine7430]

My Rb20det had the same exact symptoms, so what I did was check the spark plugs. From checking the spark plugs I found that the number two plug had not been firing as it had fuel on it and was very clean. I then took off the coil rail and took off the crank angle sensor and turned the car to run after removing the fuel pump fuse. I began to spin the crank ange sensor with only the number two coil connected and a spark plug inserted I noticed that there was no spark. Using my multimeter I check voltage on power wire and sensor wire when spinning it didnt read right. knowing that wiring was good I swap ecu's which I happen to have handy and tried the spark test again, and had spark.

I suggest a similar test if someone has this problem as my issue turned out to be the ecu.