airtraffic

Hi there!


'87 944 N/A with 77K miles.. Started out with the typical rough idle. I also had a very noticeable hesitation right around 2800 rpm. Changed spark plugs, checked plug wires. Cap & rotor have less than 10K miles since new. Timing checks good.

I did notice the throttle cable seemed a bit stretched, so I adjusted the throttle cable by tightening it up a bit. This put cold idle up to about 1100 rpm and noticeably smoother. Hesitation was reduced. If I accelerate through the gears from a stop without doing so too quickly, the car accelerates smoothly.

Things I"ve tried;

I took the cap off of the AFM and, following the web instructions proceeded to take the electrical contacts off of the worn ceramic tracks and move them a bit to the unworn track. The AFM seemed to be in pretty good shape.


Currently, the car accelerates pretty smoothly and idles fairly well when cool to just warmed up. On the highway car is smooth at 70 - 90 MPH cruising speeds. If I'm cruising at 70 mph, 3500 rpm and smoothly accelerate, I can go from 70 - 90 pretty quickly. If I try to aggressively mash down on the accelerator, the engine will "Bog down" and act like the fuel has been cut off. If I am at say 40 - 50 mph and 2800 rpm and try to "floor it" there will basically be no power. If I accelerate smoothly from 1st gear through 5th gear, there is little to no hesitation. When I try to accelerate too quickly, I seem to have a "null point" where I have no acceleration. Usually around 2800 rpm. It seems as if I am waiting for vacuum to build up before the car will accelerate? Is vacuum involved in the acceleration process? Or, does the TPS simply send a signal to the DME for more fuel? And how is this balanced against air from the AFM? If I mash down on the gas, is the car refusing to accelerate until the DME senses enough air?

I wondered whether the TPS is like a variable resistor and sends a signal to the DME throughout it's entire range? Or does it just tell the DME whether the throttle's open or closed?

I am wondering if I need to send my DME unit in to be refurbished.


After driving to work and cruising at 70 mph average.. coming to a stop sign just off the highway, the RPM's dropped to 600 and the car bucked as I pushed down on the accelerator when I tried to quickly come away from the stop sign.


Any help appreciated!

turbo944

The TPS does have a wide open point that measures differently from part throttle. You say that if you "mash hard" it has an issue but accelerate smoothly and it works good...that might be because you aren't activating the "wide open" selection on the throttle position sensor which could be bad. Not to say that's the only thing, but it is a possibility perhaps...I know mine was good cold but when it got hot it wouldn't register properly at idle and would bog terribly trying to pull away from a dead stop.

airtraffic

Yesterday, I was cruising for an hour on the interstate coming home from work, no issues, 70 MPH the whole trip. When I turned off the highway I made sure I let the RPMs come down fairly slow.. When I pulled up to the traffic light, the engine coughed and sputtered as the RPMs dropped to 200 and the engine about died. I gave it a bit of gas to bring the RPMs back to about 1000. The car stabilized and was fine for the remaining 10 minutes of stop & go driving.

turbo944

That sounds like an air or vacuum leak maybe there....the shop that did my belts last time didn't tighten up a LOT of things on the airbox or intercooler or ANYTHING well and stuff was blowing off....while driving it didn't manifest, but let off the throttle quick and yes...it would die or nearly so from the unmetered air. One easy place to start at least!

mytrplseven

Boy have I chased my tail on stuff like this over the year. I'll offer my observations from all that I've done and found:
1. start with vacuum system test. My test was quick and cheap. Buy a 2" PVC cap at the hardware store and tap an air fitting into it. Put the cap into the input side of the "J" boot and apply no more than 10 psi of air to it. Get a spray bottle and make a solution of water and liquid soap. Spray all the vacuum line fittings around the engine compartment (including the top of the throttle body). Note: there's a couple of hard to see fittings: one under the "J" boot, a couple under the intake manifold and one next to the battery on a big cannister. Find the bubbles, find the leaks. I replaced the seals in the throttle body and a couple of leaky hoses that were old and loose.

2. Clean the TPS and AFM connectors. On the subject of the TPS, there's a cam on the internal part of the switch that makes the wide open throttle (WOT) contacts send a signal to the DME. If these contacts are aged you may get a contact sometimes and sometimes not. I'd recommend replacing the TPS to fix that for sure.

3. Check your Fuel Pressure Regulator (pull vacuum hose off and check for smell or obvious indications of gas in the line). For me, I ran the complete fuel system static pressure checks per Clark's Garage. Autozone will loan you the guage kit necessary to do this. I had a stumbling acceleration issue and found out, after all the other checks to be a fuel pump that made the pressure but didn't provide sufficient fuel flow. When's the last time your fuel filter was replaced?

4. Check for loose connectors on the fuel injectors. I pulled my injectors and repaired the connectors and rebuilt the injectors and replaced the intake manifold gaskets while I was at it.

5. Consider replacing the AOS seals. They have been associated with "strange" engine symptoms not clearly tied to anything specific.

I know that's a big list but I offer it as a suggestion of some things you may not have considered. Good luck in finding your bug.