Why is my Q surging?!?

[96'er]

Since last weekend my 1996 Q45 has been surging while driving, I can be on the highway, in town or pulling away from a stop. All this started after refueling the car at a BP station, premium fuel.

IMO, the motor acts like it is fuel starved. The motor starts to surge and buck and then the tach begins to flucuate. The duration of the surging last approximately 15-20 seconds and then it runs normally.

Other than this problem the car has been trouble-free motor-wise. The only maintenance I have done is a K&N air filter and new NGK factory spec'd spark plugs. Oil is changed every 3k miles.

Any ideas as to what is going on with the motor or has someone experienced something similar?

[elwesso]

check fuel pressure. report back with readings.

[96'er]

How do I check fuel pressure?

Also, I cleaned the MAF and throttle body to make sure that those two are not the culprits.

[maxnix]

T a fuel pressure gauge in after the fuel filter.
Modified by maxnix at 7:53 PM 11/6/2007

[AlabamaDan]

Vaccum leak? Do you hear any hissing? There's a little short hose behind the EGR valve from the plenum to something under the plenum. I've seen a number of Qs (including mine) develop a hole there and it affects the idle and running.

[jjbuzzman]

My 91 began the surging routine, but my surges were more like 3 or 4 seconds. Although I've not seen these symptoms associated with a fuel pump control unit, that's what my problem was. As soon as I changed out the FPCU the surging disappeared. I also changed out the fuel pump but by trial and error I had determined the FPCU was the culprit.

[Haitian_King]

How are your injectors?

When I had a bad one, I'd be on the road and if accelerating through a slight bend (like 45 to 55) the car just started jerking and vibrating. I also had a rough idle that shook the car noticeably.

I hope you get to the bottom of your problem and it isn't too expensive to remedy.

[96'er]

The car idles great and since I have cleaned the MAF and TB I replaced the fuel filter as well and the car doesn't seem to be acting up right now.

If it acts up again, I will check the fuel pressure and injectors next.

I appreciate the feedback.

[1990QOwner]

T a fuel pressure gauge in after the frul filter.

At 60 PSI I don't think tape is going to hold a pressure gauge on. I would go to a shop and they could do it in a few minutes. When I tested mine than I went to the local hardware store and just bought a cheap but accurate air pressure gauge and a barbed fitting that would fit the fuel line. I hose clamped it after that and than got a pressure reading. The fuel ruins the gauge (if it is a cheap air one) but they are quite cheap and are accurate for the one time.

[goody90q45]

Pull the codes off the ECU. If there are none it's probably a fuel issue.

[Haitian_King]

What he said.

Goody has never steered me wrong. His advice is extremely helpful.

[DrewQ45]

I have a few FPCUs on the board if needed...

zerothread?id=280391

[stormmotor]

Mine did that the other day after replacing a stupid two inch fuel line under the plenium. It turned out to be the throttle cable wasnt adjusted properly.At least thats what was causing mine to surge and it also Idle at 1,500 to 2,000 rpm's.. Try checking that out.