bucking

[q45frustrated]

OK I bought a used 1996 q45 and I love it but it has the bucking problem. I changed maf and air filter and it was fine til today when I turned it off for an hour and started it again. Bucked and it stalled wouldn't idle and hesitated and wouldn't rev up even in neutral. I have seen old posts but nothing recent. Has anyone got a definitive answer to this problem ?? Help

[N/A Q45]

If it is a maf problem unplug the maf and if it runs better you've more then likely found the problem-
Sounds like a vacuum leak though, have you had any hoses off or anything?

[q45frustrated]

maf been replaced twice. I'll check hoses tomorrow but it runs fine when it's cold.

[N/A Q45]

When it's cold it runs richer so if you have a vacuum leak it won't seem as bad until it warms up.

And unless you got 100% brand new maf don't rule it out. It takes 4sec to unplug it and check

[q45frustrated]

it is new but ill ck it. where should I ck for leak

[N/A Q45]

Some leaks you will be able to hear, small ones will have a high pitch but quiet sound and others you will hear very clearly. Can check for leaks by looking but in stock form there's quite a few to check, it's easier to just get a spray bottle and squirt water on the vacuum lines and listen to hear a change in the idle or the water being sucked in, the better way is to use carb cleaner and do the same but -only- if you know what you're doing, don't want to spray the wrong thing or w.e and cat h s*** on fire. But the carb cleaner makes it easier as it provides a bigger change in the engine idle.

[Infinitiguy19]

Don't spray water to find vacuum leaks! Just check the vacuum pressure at idle.

[q45frustrated]

how do I do that

[N/A Q45]

Don't spray water to find vacuum leaks! Just check the vacuum pressure at idle.

Lol alot of people don't have a vacuum gauge or even know what the stock vacuum should be. Do you?-

[q45frustrated]

no

[N/A Q45]

My question was for infinitiguy. You can do what he said but it is very pointless if you have a vacuum leak the gauge isn't going to be like '' heyy! I found your vacuum leak it's right over there'' lol

[Q451990]

Yeah... skip the water. Brake parts cleaner is my combustable of choice for hunting down leaks. If it gets sucked in you'll notice the idle rise. Just avoid spraying anything that's plastic that you don't want messed up. It can really attack some kinds of plastic.

Heath

[q45frustrated]

unplugged the maf and car stalled now what ?

[N/A Q45]

Maf is good.
Try what I said about the water or if you're careful carb cleaner.

[q45frustrated]

so where r vacuum lines and are they rubber ?

[N/A Q45]

That's the fun part as there are alot of vacuum lines.. but you can start by spraying all around the TB (throttle body) where there's lines, where the brake booster line hooks up to the plenum and its other connection. The egr is also a high risk of have a crack in its lines (its on the right side of the TB with a steel tube going into it) , around where each runner bolts to its bottom half (in the middle of each one) and the air control valve at the rear of the engine (it's mounted on the intake runners)

[N/A Q45]

Try that and let me know.

[Infinitiguy19]

I can post whats been said many times over by Q45Tech or one can search.

Vacuum Leak Testing
The only place I use is the vacuum line at the fuel pressure regulator ....rear of engine down in
valley....hard to get to. We are talking about a Q45 but on most cars this is the best place to get
max vacuum. You should use a tee because if you disco the line from regulator the idle fuel
pressure will rise by 10 PSI and the injectors will try to flow 13% more which can lower pulse
width due to feedback control

7169 Vacuum Leaks and Testing http://www.asashop.org/autoinc/MAY/Tech2tec.htm

7173 A simple vacuum gauge connected [or teed] to the vacuum line feeding the fuel pressure
regulator should read 17-18" minimum at idle warm or cold. If you disconnect the vacuum to
pressure regulator the fuel rail pressure will increase from 34 PSI to around 44 PSI causing a
13.7% increase in flow the ECU should respond by reducing the idle pulse width from around
2.2 milliseconds to around 1.95 - 2.0 milliseconds. Remember the ECU is designed to maintain
a preset idle rpm so more/less air or more/less fuel are all it has to work with.

One thing to look for would be an air or vacuum leak that is getting into the air intake system
after the MAF sensor. When the car is warm, the ECU does not enrich the fuel mixture. If air is
getting into the system that is not measured by the MAF sensor in the intake, the extra air leans
out the mixture. This usually results in poor warm start and idle.

Check to see if there is a loose or cracked vacuum hose or clamp. One way mechanics check
for vacuum leaks is to spray a little gas (butane or methane or ?) in various spots and see if the
idle RPM goes up and it smoothes out. If so, that indicates that the gas got into the intake
system, and that air is sneaking in through that spot.

Have you recently disassembled the intake system or vacuum tubes? If so I would check there
first - maybe you forgot to tighten a clamp or replace a vacuum hose. Make sure all vacuum
hoses are connected, since this is an easy way to create an air leak in the system. See
Q45tech's response to recent inquiry about cold start problems. I don't know if crank angle
sensors would show up only in warm start or not. A bad coolant temperature sensor might. I do
think it is a good clue when the problem is only when warm and suspect that something is
making the mixture too lean. I had exactly those symptoms once when I forgot to reconnect a
small vacuum connection.

Bob

A simple vacuum gauge connected [or teed] to the vacuum line feeding the fuel pressure
regulator should read 17-18" minimum at idle warm or cold. If you disconnect the vacuum to
pressure regulator the fuel rail pressure will increase from 34 PSI to around 44 PSI causing a
13.7% increase in flow the ECU should respond by reducing the idle pulse width from around
2.2 milliseconds to around 1.95 - 2.0 milliseconds. Remember the ECU is designed to maintain
a preset idle rpm so more/less air or more/less fuel are all it has to work with.

Q45Tech

[N/A Q45]

And that is some good info^

[black g50]

I also chased that problem,Replaced everything recommended.It came down for me to themastat and both rad caps.Go figure

[q45frustrated]

took it to the dealer replaced the mafs Friday so far so good Over $900 !!

[BCC93QT]

Hoped they both praised you and laughed at you for bringing it to a "dealership"

[N/A Q45]

Was probably just the maf connector then. That was a fail and waste of $$.

[mrpeeb240]

I finally cured my bucking Q!!!. After many parts and lots of suspect hoses replaced it turned out to be seal at throttle body to intake pipe. Replaced with 3"-3.5" silicone coupler and boom smooth sailing. Now to fix primary ignition signal code, its been on since I replaced coils, TCS and slip lights on steady and of course knock sensors

[N/A Q45]

And just think you could have found that with a $8 can of carb cleaner-


Good thing you listened to the people who were trying to help you on here-

[mrpeeb240]

Funny I tried that trick many times with every combustible and it never worked. Found it by accidentally leaning my elbows on the intake pipe while messing around with a harness while the car was running. Idle leaned out and died