1994 Q45: Fluctuating idle and loss of power after warming up engine

[DORIMON]

Right after starting up my 1994 Q45, driving for like 5-10 minutes it runs perfect, shifts smooth, and pulls very strong all through the powerband, but once the engine temp needle is at normal operating temp. It feel like its running on only 7 cylinders. The idle isn't any worse, it just feels like there's a delay in throttle response when trying to accelerate. Feels like the transmission is is struggling to downshift at a certain throttle opening and when flooring it, the tach needle going through the powerband is not as quick. Could this be transmission temp or possible coolant temp sensor failure? There are no check engine codes except for 0505. What also sucks, is that there's some smoke coming from the engine only after it has warmed up, I can't really pinpoint exactly what part of the engine its coming from, but it can be seen coming faintly from the sides and behind the engine. What seems to be the problem here?Update: After driving to work today which took about 30 minutes/30miles, before shutting the car off the idle was fluctuating between 650 and 800rpms, when most of the time in the past when it was warm it would be steady at 650rpms. Anyone know whats going on?

[maxnix]

What is the general intake path maintenance history?

What is your fuel pressure?

[Q45tech]

As always first test the fuel pressure at idle, at cruise and at WOT 6,000 rpm driving.

Then wiggle the MAF connector lightly looking for changes, tap on top lightly or just swap MAF with your spare unit.

Ohm injectors.

[elwesso]

definitely check what they say, and the next thing would be to see if the car is running hot....

[silkysmoothyjud]

sounds like a combination of things, idle fluctuation, MAF... vibration=injector 99.9% you wont always find the one doing it just by ohms, trial and error. If you are having a rough first to second gear shift then it is an injector or two or three FOR SURE!!!! Ive had so many problems with injectors I am becoming a pro. I have the back of my plenum secured with little c-clamps for easy removal, I can change any injector under the plenum in about 15 minutes and I use 1 and 2 to test used injectors. My suggestion, buy two new injectors and start trouble shooting. You'll be shocked how rough one bad injector can make your idle. When inspecting your injectors, check for color, it might help you. I found a bad one because all of my injectors are purple, except one (NOW THEY ARE ALL PURPLE). The bad injector still ohm at 12.2. Also, a vacuum leak (more like a restriction) can cause a low steady rough idle. Plenum to plenum hoses can cause this (I'm speaking from experience). Look at the hoses next to the throttle body, that hose that sits at a 90 degree angle. Is there a ninety degree angle in that hose? If not, it will cause a Q to idle at 500 roughly after warm up. Take a pair of pliers and squeeze that pinch in the hose and the idle will go to 750 instantly. The previous owner of my car totally rigged that hose, resulting in rough idle that was steady at 500 rpm. That was a tough one, thought Id share it since it took me about three months to find it..... Thanks NICO

Modified by silkysmoothyjud at 10:23 PM 6/14/2007

Modified by silkysmoothyjud at 10:25 PM 6/14/2007

Modified by silkysmoothyjud at 10:28 PM 6/14/2007
Modified by silkysmoothyjud at 10:31 PM 6/14/2007

[ghrigter]

I have a Q 1995, with about the same problem. However, it is very intermittent. I changed the in-tank pump about a year ago.... no humming anymore in the back..... but occasionly... car stalls agin when hot and I have to rescue HRH my wife. I can drive the car home holding the RPM at about a 1000 After the car has been sitting overnight everything is fine again..... till the next time, what can be as far as 2 months apart. The problem is impossible to re-create by itself. Checked connections... Cleaned MAF etc. I cannot find the vacuum hose near the Throttle body as you describe... is it possible the sent a pic which shows the location.....?Thanks ahead!Gerrit

[goody90q45]

I have a Q 1995, with about the same problem. However, it is very intermittent. I changed the in-tank pump about a year ago.... no humming anymore in the back..... but occasionly... car stalls agin when hot and I have to rescue HRH my wife. I can drive the car home holding the RPM at about a 1000 After the car has been sitting overnight everything is fine again..... till the next time, what can be as far as 2 months apart. The problem is impossible to re-create by itself. Checked connections... Cleaned MAF etc. I cannot find the vacuum hose near the Throttle body as you describe... is it possible the sent a pic which shows the location.....? Thanks ahead! Gerrit

Gerrit- Cut and paste this into your own thread. We don't want to get the two issues confused. Sounds like your fuel pump control unit but let's talk about it in your own post.

[silkysmoothyjud]

I think goody is right, said vacuum hose problem will cause a low idle and vibration at idle after the car is warmed up. The bad idle will be worse in park. It will come and go after the rubber in the hose has expanaded due to heat (It's freakin hot in the mid west right now, hence my discovery). After driving for a while, said hose could cause an occasional stall after startup. However, the stall will not strand you. It will not cause the car to idle at 1000rpm after warm up, ever. FPCU (especially if you let your FP hum for a long time) or MAF more than likely to blame.... (goody knows more about this than I do)....I'll post a picture once I get her back, but she's getting her hood painted now (I'll be able to read a book in her reflection!). If you look directly at the plenum throttle body, look about two inches to the right. If that medium sized hose is pinched (the hose is bent causing a restriction), it will be easily identified, and subsequent problems wont happen in one month intervals, it will happen all the time....

Modified by silkysmoothyjud at 11:00 PM 6/18/2007

Modified by silkysmoothyjud at 11:09 PM 6/18/2007
Modified by silkysmoothyjud at 11:11 PM 6/18/2007