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E90 335i surging at low rpm

Car surging at rpm between 1000 and 1500rpm

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2 Answers

What is causing the fast Idle and slowing down


well gee, there are 50 reasons.
did you scan the PCM yet, if not ,why not?
when the idle surges, that means.
NO RPM ranges stated, if super low rpm check EGR.

1: engine lean and ISC dead, or cant handle the huge engine power drop..The PCM can even make this worse!, buy hunting the ISC to find spec, idle and failing... to...
2: or any of 50 other things causing huge engine power drop and PCM can't maintain idle controls.
super lean burn.(bogging)
super rich burn, misfire for 50 reasons.

i cant hear your engine,nor feel it, or see it shake from gross misfiring.
no can i drive it and see/feel power loss,
can I?
asking net bunny's this (blind as bats)
is "OVER THE TOP" no?
so here , ill toss the dice for you
and guess gross misfiring.
ever get a tuneup this decade, if not bingo , no?

and the others...

http://jeepdied.com/Misfire101.html

link even has the 50 cause list, to show the futility of guessing!
we do 1 to 10 tests. and find it.
for sure.

as you can see EFI systems are complex.
gue$$ is not only expensive but can net you 2 problems easy.

Feb 05, 2016 | 2002 Jeep Grand Cherokee

1 Answer

97 toyota surges at an idle


(which engine. ?????)_
as always check all fuses. and scan the ECU for DTCs. first.
there is no need to fix OBD2 cars like 1980 cars (hard rows to hoe)
it can be 2 problems this......
lets fix the easy one first. idle. (and hope for moving issues to fix for free) it idle car is parked, so is 100% safe tests. (not moving)

so it surges at idle.
questions.?
1: hot or cold or both.?
2: low extreme RPM and high at idle.

400 to 800 RPM? surge.
1000 to 2000. what? numbers tell the tale.

first off, idle is the last thing to work right on any engine.

there are many ways to find what is wrong.
fix idle surge way.
i make sure that the engine holds closed LOOP status.
hot idle, if not , i fix that first.
keep in mind if not in closes loop and lean
all lean engine surge and guess what the ISC will add to the surge
because idle is way too slow, so the ECU open the ISC wider
and wider and its still too slow, so the ECU resets the ISC
this cause a worst hunt (surge)
the ECU adjust spark time and the ISC to get 800 rpm. (spec. look up yours)
so say , i see closed loop failed, OBD2 scan page 1
i look at the O2 sensor an its stuck lean.
if stuck lean and it really is (o2 bad?) then its lean and it will surge
.
examples.
1: i find 02 sensor bad, (only effects idle and light steady cruise)
2: i find fuel pressure at 15PSI , hopeless low .
3: i find all injectors clogged. and lean.
4: with MAF EFI, ( i find maf reading too low, (dirty) causing lean.
5: if MAP car, i find the MAP stuck hard high vacuum causing lean.
not knowing what engine you have or the idle hot surge range,
i can not go farther.

the driving bog tells me,
1: scan the ecu ,get DTCs; do that first.
2: clean MAF if car has one, ask how..
3: check fuel pressure.


my guess is engine is lean. and starving for fuel all the time.
cept WOT.

MAF cars starve for fuel if there are any vacuum leaks.
MAP cars do opposite, they race fast with 100% full power.
MAF is air density EFI
MAP is speed density EFI.
apples and oranges diffr. so what engine.


Jan 07, 2014 | 1997 Toyota Tacoma

1 Answer

Throttle surge at idol


surge, great post, what engine displacement.
open hood (my answers are USA only) look up, see big white
sticker that is the engine vacuum and type engine sticker)
surge hot or cold? engine.
if it surges hot, that means :
1: ISC system out of control , it job is to stop surge and 5 more things.
2: the engine is way lean and cause ISC to loose control

just 2 reasons, and can be 50 things. wrong.
is the CEL lamp out running> if not, pull the DTC codes and post them. (all)
as a mech ,we find out which it is.
(i make sure my engine can hold closed loop at idle , if not and lean it will surge. (may)
we make sure the ISC works ok (not sticking, clean it)
and then test to see , that if by my forcing it closed, by hand (ask)
i can get way below 800 RPM. most do 500 but 600 is ok.
if rpm stays above 800 closed, that means you have huge
vacuum leak or TV blackage (too thight throttle cable?)

finding vacuum leaks can be horrific, task .
there are many tricks (and tests) to do this, ask.

see that logic above, If I the mech, can not drop rpm below 800
by hand, then no ISC on earth can. not now or ever.
and proves the induction has huge air leaks
or some dolt set the spark timing 20 degrees advanced.
see it.
so as always , a tuneup is first, then as always , i always check timing,and for proper advance rates.
advances engines at idle race way too fast and the iSC will just go NUTS.

ISC = Idle speed controller , that valve that has wires.
the IAC is a thermal device and no wires and it too can stick open
when the IAC sticks open the ISC goes , yes, nuts,
nuts can be surge (ECU is hunting it)
or just racing way too fast hot, say 1500 rpm.
a slow RPm can be a stuck open EGR (50k service point)
lean will cause too low.
too rich , misfires and too low
the ISC is the last thing to work right, all else must be good.

what does your CEL lamp do?

PS: most cars, if the ECU/PCM enters Limphome, it cuts all idle controls. again, the CEL lamp. glowing while running.../????

Nov 28, 2013 | 1994 Honda Civic Del Sol

1 Answer

Increase then decrease idle when engine is cold especially


cold engine idle surge. (problem)
RPM range of surge not stated
300-700 or 800 to 1500? (range is critical to diagnosis)

bad fuel
running summer fuel in winter (running old fuel?)
needs a tune up bad, see the list in the operator guide.
idle speed controller,sticking or EGR valve same. (clean them)
location not stated, so cant guess about local air temps.?
no other symptoms, lack of engine power? etc?
was it ok last week, or better, when was the last time it was OK?
1week, 1year?
surge , causes, on a tuned engine might be:
1: too lean. so lean the ISC can not control idle. rpm low, stalling
2: too rich, flooding, stalling, spark plugs foul (look at them)
3: weak compression in 1 or more cylinders.
4: bad spark.
5: air leaks, in the plenum causing , ISC to lose control.
why high RPM?

especially?
well that means it fails hot too.
and there is a simple tests. for hot surge.
is engine fully hot? 180F and holds solid there?
say rpm is about 800
and you turn on head lights, heater fan and (not AC) and defrost.
the RPM must hold or the ISC is failing.
ISC -= idle speed controls. (all EFI has this function)

Oct 28, 2013 | 1996 Honda Prelude

1 Answer

Has low power, surges @ cruizing speed, rough idle (code 32)


You can remove the egr and see if it has been sealing,and if it still moves.

Jan 29, 2010 | 1993 GMC Sonoma Club

3 Answers

Low rpm's in idle when heating/cooling system is on & surges.


Check your EGR or your Idle control Valve. This can cause a problem with your irratic idling

Apr 17, 2009 | 1995 Ford Explorer

1 Answer

1995 ford bronco 5.8l surges while going uphill


check vacume lines, knock sensor, and air intake sensor

Feb 18, 2009 | 1995 Ford F350

1 Answer

Surging and loud whistling noise


Sounds like a vacuum leak. Check all vacuum hoses on the intake, throttle body, etc. Sounds like one cracked or came off. Post back if you have any questions. Hope this helps.

Feb 08, 2009 | 1996 Chevrolet Impala SS

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