Hello. 2000 Ford E-150, 5.4 L, 166K miles, custom conversion van, original owner, better than average maintenance for 16 years.
Months ago, engine
started hesitating/stumbling on right turns only, from stop to go. Less frequent to more frequent over time. Weeks ago, stalled for first time, and then a few times since. NOW DANGEROUS. Also now hesitating on straight starts from stops, not only on right turns.
My research so far suggests many potential causes, and most look to be beyond the reach of me and my tools, but I decided to check here first and maybe save a few thousand Ford dealer bucks?
One potentially related item (vacuum). Some months ago, lost control of the A/C vents. My online research found the problem, vacuum leaking somewhere, probably the "surge" tank, which is almost inaccessible. Followed a video on YOUTube how to bypass the tank and it worked! But now I wonder if it affected some other vacuum system that is causing my hesitation/stalling problem? Service Engine liight does NOT come on. Scan meter was used by a parts dealer and no problem codes were found.
Some possible causes I have read about are:
-dirty or bad mass air flow sensor
-dirty throttle body
-coils (replaced 3 or 4 already, but symptoms were totally different)
-idle air control valve
-intake air temperature sensor
-throttle position sensor
-low EGR flow
The trouble is, I do not have experience with modern engines and no specialized tools. I do not want to just start replacing or removing and cleaning parts "willy-nilly" which can be expensive, dangerous, frustrating and ineffective. Rather, I am hoping that an expert here can apply some probabilities to the possibilities to save me some time, effort and money, and guide me through a fix. This is our only vehicle so it cannot be out of service for long periods, but a short-term rental car would be OK for a while.
Summary of key points:
-hesitation/stumbling was limited to right turns only from stop to turn. was that way for months. very occasional to more often, but never always.
-recently began happening on straight ahead starts from stop.
-recently totally stalled in traffic a few times.
-no engine light, no codes, no other problems.
-otherwise starts fine, runs fine.
-over the years, have had various system flushes, fluid changes, injector cleanings, throttle body servicing, etc., all done by auto shops. regular maintenance, oil changes, etc., done regularly.
-uses 1 quart of oil every 750 miles. no smoking, but exhaust
seems more noxious than normal.
-began using partial synthetic, then full synthetic oil many years ago, after passing 100k miles..
Thanks in advance for your attention to this.